Unit 1: Human Impact on the Environment

This unit explores how human activities alter ecosystems, affect biodiversity, and contribute to environmental change on both local and global scales.

Core Topics

HIPPO (Habitat change or destruction, Invasive alien species, Pollution), climate systems and processes including glaciation and interglacial periods, greenhouse gases and their sources, the greenhouse effect, carbon footprint, ecological consequences of global warming, FACE trials, the El Niño effect, red tides, eutrophication and algal blooms, acid rain, pollution management, salmon farming and the ISA virus, and conservation strategies.

H.I.P.P.O.

“I think Moto Moto likes you.”

The acronym H.I.P.P.O. does not refer to the animal, but instead represents the five main human-driven causes of biodiversity loss and global species extinction:

• Habitat loss
• Invasive species
• Pollution
• Population growth (human)
• Overharvesting

Habitat Loss

The loss of both terrestrial and aquatic habitats greatly affects biodiversity. According to the IUCN, approximately 85% of species classified as Threatened or Endangered are primarily affected by habitat loss.

Terrestrial habitat loss occurs due to urban development, resource extraction, and agriculture. Converting undeveloped land into urban areas deprives organisms of their natural habitats, while activities such as mining, logging, and oil drilling damage surrounding ecosystems.

Around 15 billion trees are cut down each year. Deforestation also reduces the ability of forests to act as carbon sinks, limiting carbon dioxide uptake through photosynthesis.

Agricultural expansion is a major driver of habitat loss, particularly when unsustainable practices such as slash-and-burn farming are used. These methods reduce soil fertility, forcing further deforestation. During the 1990s, nearly 70% of deforested land was converted into agricultural use.

Aquatic habitats include oceans, rivers, lakes, wetlands, and bogs. Deforestation increases soil erosion, leading to sediment runoff that blocks sunlight in shallow waters and disrupts organisms such as coral reefs.

Wetlands and estuaries act as breeding grounds for many fish species, but dredging and land reclamation disrupt life cycles. Peat bogs are also important carbon sinks, as acidic conditions prevent organic matter from decomposing and releasing carbon into the atmosphere.

Even small-scale actions such as raking leaves can disrupt forest floor ecosystems by removing nutrients and shelter needed by insects and small animals.

Invasive Species

Invasive species are non-native organisms that negatively impact ecosystems. Examples include kudzu vines and cane toads. These species often outcompete native organisms for resources such as food, space, and sunlight.

Invasive species are typically introduced intentionally or accidentally through human activities such as trade, travel, agriculture, and the exotic pet trade.

To be classified as invasive, a species must:

• Proliferate and reproduce rapidly
• Adapt effectively to the local environment
• Outcompete native species
• Cause harm to local ecosystems

Invasive organisms are not limited to animals; plants, fungi, and microbes can also become invasive.

Consequences of invasive species include environmental damage, threats to human health, and economic losses. Invasive species can cause up to $1.4 trillion in global economic damage by affecting industries such as fisheries and forestry.

An example is the black wattle tree, which rapidly depletes water sources despite being introduced for timber production.

Species may be introduced intentionally, such as the cane toad in Australia for pest control, or accidentally, such as zebra mussels transported in ship ballast water.

The rapid growth of kudzu in less than one year.

Kudzu vines are an invasive species commonly found in North America, despite originating from Asia. They grow rapidly over trees and other plants, smothering them and blocking access to sunlight. Kudzu also outcompete native plants for root space, preventing new saplings and shoots from establishing.

Kudzu was originally introduced as an ornamental plant and later extensively planted to reduce soil erosion. This intervention proved to be highly ineffective and environmentally damaging.

Grey squirrels are another example of an invasive species. Native to North America, they were introduced to the United Kingdom from the 1890s onwards. Compared to native red squirrels, grey squirrels are larger, more robust, and better adapted to competing for food and habitat.

Grey squirrels also carry the squirrelpox virus, to which red squirrels have little resistance. This disease has significantly reduced red squirrel populations. Additionally, grey squirrels can digest tannin-rich foods such as acorns more efficiently, giving them a further competitive advantage.

Crayfish are freshwater crustaceans that exist in both native and invasive varieties. In some regions, native white-clawed crayfish are threatened by invasive red-clawed crayfish. The invasive species outcompete natives for food and shelter and transmit crayfish plague, which is often fatal to native populations.

Controlling the Spread of Invasive Species

• Clean, Dry, Disinfect: Thoroughly cleaning boats and equipment before moving between water bodies reduces the spread of invasive organisms such as zebra mussels.
• Do not release exotic pets: Releasing non-native pets into the wild has led to invasive populations, such as Burmese pythons in Florida.
• Plant native species: Encouraging native vegetation supports local ecosystems and reduces invasive spread.
• Biocontrol agents: Introducing natural predators or pathogens to control invasive populations.

Pollution

Pollution refers to the introduction of harmful substances into the environment. Plastic pollution is one of the largest contributors to land and soil pollution. Plastics are artificial polymers primarily derived from petroleum.

Plastics: Advantages and Disadvantages

Pros:

• Cost-effective to produce
• Readily available
• More durable than alternatives such as paper or cardboard
• Recyclable in some forms (thermoplastics can be melted and reused)

Cons:

• Not biodegradable
• Cannot be decomposed by microorganisms
• Harms living organisms
• Releases toxins and carcinogens into ecosystems

Plastic pollution can be reduced using the 4Rs: Refuse, Reduce, Reuse, and Recycle.

Impacts of Plastic Pollution

Social:

Encouraging individuals to switch from plastic to sustainable alternatives is challenging due to cost, convenience, and habit.

Economic:

Plastic products are often cheaper than alternatives such as glass, making them more accessible to low-income households. Recycling programs can provide financial incentives.

Environmental:

Plastics persist in the environment and can break down into microplastics. Aquatic organisms may ingest plastic debris, mistaking it for food, leading to injury, suffocation, or death.

Ethical:

The use of plastic raises ethical concerns due to long-term environmental damage. Some alternatives, such as paper straws or plates, may also have significant environmental costs through production and waste.

Bioaccumulation and Biomagnification

Biomagnification is the process by which toxins become more concentrated at higher trophic levels within a food chain.

This occurs with substances such as pesticides and fertilizers. DDT (dichlorodiphenyltrichloroethane), once widely used as an insecticide, accumulated in bald eagles, causing eggshell thinning and reproductive failure.

Mercury can also biomagnify through aquatic food chains. Humans consuming contaminated fish may develop Minamata disease, which can cause neurological damage and delayed brain development in children.

Only approximately 90% of energy is transferred between trophic levels, with around 10% lost as heat. As a result, organisms must consume large quantities of food, increasing toxin intake at higher trophic levels.

Bioaccumulation refers to the buildup of toxic substances within a single organism over time.

Bioconcentration describes the accumulation of toxins within all aquatic organisms in a specific environment.

Populations

A population consists of all organisms of a single species living in a specific area at a particular point in time. This differs from a community, which includes all populations of different species in an area, and an ecosystem, which includes both biotic and abiotic components as well as their interactions.

Changes in population size can be explained by four main factors:

• Competition: Organisms competing for food, territory, or mates may result in weaker individuals failing to reproduce or being eliminated.
• Disease: Disease outbreaks in non-immune populations can rapidly reduce population size until immunity develops.
• Predation: Increased predator numbers result in higher prey consumption and a reduction in prey population.
• Food scarcity: Limited food availability leads to starvation, with weaker organisms dying first.

Predator and prey populations are inversely proportional. An increase in prey population is followed by a delayed increase in predator population, as predators require time to reproduce in response to food availability.

Similarly, when prey populations decline, predator populations initially remain high before gradually decreasing due to food shortages.

Population Growth Curves

Population growth can be modelled using a sigmoid (S-shaped) curve, commonly observed in controlled bacterial growth.

The lag phase represents the period during which organisms adapt to their environment before reproduction begins.

The exponential growth phase follows, where the population increases rapidly as organisms reproduce at maximum rate.

As resources become limited, the population enters the stationary phase, where growth rate slows and population size stabilizes.

If the population exceeds the environment’s carrying capacity, resources become scarce and the population declines during the death phase.

The Greenhouse Effect

The greenhouse effect is the warming of the Earth’s surface due to greenhouse gases trapping thermal energy in the atmosphere. Earth’s atmosphere is composed of approximately 78% nitrogen, 21% oxygen, and around 1% other gases, including greenhouse gases.

Energy from the Sun reaches Earth as electromagnetic radiation. After absorbing this energy, the Earth’s surface radiates heat back toward space. Without an atmosphere, much of this thermal energy would be lost.

Greenhouse gases such as carbon dioxide, methane, nitrous oxides, and chlorofluorocarbons trap heat reflected from Earth’s surface. These gases re-radiate thermal energy back toward Earth, increasing surface and atmospheric temperatures.

This natural effect is essential for life. Without greenhouse gases, Earth’s average surface temperature would be approximately −18°C, making the planet uninhabitable.

Human activities, particularly the burning of fossil fuels, have increased the concentration of greenhouse gases in the atmosphere. This intensifies the greenhouse effect and causes excess heat to be trapped.

Even small increases in global temperature have severe consequences. Recent records show global temperatures exceeding previous averages, resulting in widespread environmental impacts.

• Accelerated melting of ice caps and glaciers
• Rising sea levels
• Increased risk of extinction for temperature-sensitive species
• Coral bleaching due to warmer oceans
• More frequent and severe natural disasters
• Spread of disease-carrying insects into new regions

Carbon Footprint and Carbon Cycling

A carbon footprint is the total amount of carbon emissions released into the atmosphere by an individual, activity, or organization. Carbon emissions contribute directly to the greenhouse effect.

Carbon-neutral activities neither increase nor decrease atmospheric carbon levels, such as walking or cycling instead of driving.

Carbon sinks are systems that absorb and store carbon from the atmosphere. Examples include forests, oceans, and afforestation efforts.

Global Warming

Global warming is the long-term increase in Earth’s average surface temperature since the pre-industrial period due to human activities, particularly fossil fuel combustion.

While climate change can occur naturally, global warming is accelerating these changes at an unprecedented rate, leading to widespread environmental, ecological, and societal impacts.

Glacial and Interglacial Periods

Glacial and interglacial periods are long-term climatic phases lasting thousands of years. Glacial periods are characterized by colder global temperatures and the advancement of glaciers, while interglacial periods are warmer intervals during which glaciers retreat.

These periods alternate over geological time and are driven by several interacting factors:

• Continental drift: The movement of tectonic plates alters the position of continents relative to the equator and poles, influencing regional and global climate patterns.
• Volcanic activity: Volcanic eruptions release heat, ash, and aerosols into the atmosphere, which can temporarily alter global temperatures.
• Astronomical factors: Variations in solar radiation, Earth’s orbital shape, and axial tilt affect how much thermal energy reaches Earth (Milankovitch cycles).
• Atmospheric factors: During glacial periods, higher dust levels in the atmosphere reflected more heat back into space, while greenhouse gas concentrations such as carbon dioxide and methane were lower than during interglacial periods.

FACE Trials and Carbon Dioxide Concentration

FACE Trials (Free-Air Carbon Dioxide Enrichment)

FACE stands for Free-Air Carbon Dioxide Enrichment experiments. These experiments are used to predict future rates of photosynthesis and plant growth in response to increasing atmospheric carbon dioxide concentrations.

FACE trials are particularly important due to rising greenhouse gas emissions caused by fossil fuel combustion and deforestation.

Procedure

FACE trials are conducted in open-field environments. Carbon dioxide is released into the air using large circular arrays of pipes surrounding vegetation. Sensors, valves, and wind vanes monitor CO₂ concentration and wind direction to ensure even gas distribution across the study area.

Control plots exposed to normal atmospheric CO₂ concentrations are used for comparison.

Advantages of FACE Trials

• Provide realistic insight into ecosystem responses to elevated CO₂
• Account for uncontrolled variables such as light, water, and species interactions
• Allow study of large plants and trees in natural conditions

Limitations of FACE Trials

• Not suitable for short-term studies
• Extremely expensive to operate and maintain
• Environmental variables cannot be controlled

Enclosed CO₂ Experiments

Enclosed CO₂ experiments are performed in controlled environments such as greenhouses. CO₂ concentration, temperature, and light intensity can be precisely regulated.

Pros:

• Useful for short-term studies
• Allows isolation of individual variables

Cons:

• Lack ecological realism
• Do not account for competition, soil variation, or mature trees acting as carbon sinks

Variables in FACE Experiments

• Independent Variable (IV): Atmospheric CO₂ concentration
• Dependent Variable (DV): Photosynthesis rate, plant height, biomass
• Control Variables: Generally not controlled, as FACE trials aim to observe CO₂ effects under natural conditions

The El Niño Effect

El Niño is a global climate phenomenon occurring irregularly every 2–7 years in the Pacific Ocean and lasting approximately 9–12 months. It was named by South American fishermen after its frequent appearance around Christmastime.

An El Niño event is identified when sea surface temperatures in the equatorial Pacific rise by at least 0.5°C for three consecutive months, accompanied by altered atmospheric pressure and rainfall patterns.

Normal Pacific Conditions

Under normal conditions, trade winds push warm surface water westward toward Asia and Oceania. As this warm water moves west, cold, nutrient-rich water rises near South America to replace it — a process known as upwelling.

Upwelling supports phytoplankton growth, which forms the base of productive marine food webs and sustains fisheries.

El Niño Conditions

During an El Niño event, trade winds weaken. Warm surface water is no longer pushed westward and instead accumulates near Central and South America. Upwelling is reduced, preventing nutrient-rich water from reaching the surface.

This results in reduced phytoplankton populations, which causes fish numbers to decline and disrupts marine food chains.

Global Impacts of El Niño

El Niño dramatically alters weather patterns. Regions such as Indonesia and Australia experience reduced rainfall and droughts, while parts of South America face heavy rainfall and flooding.

Warmer Pacific waters increase hurricane formation and severely impact fishing industries due to the collapse of marine food webs.

El Niño events also cause marine heatwaves, prolonged periods of abnormally high ocean temperatures. These events are intensified by climate change and have led to mass die-offs in species such as snow crabs.

Marine heatwaves can also trigger harmful algal blooms, which will be explored in the following section.

Glacial and Interglacial Periods

Glacial and interglacial periods are long intervals marked by colder temperatures with glacier advancement, and warmer climates respectively.

These cycles are influenced by several factors:

• Continental drift: Movement of tectonic plates changes climate zones.
• Volcanic eruptions: Release heat and debris into the atmosphere.
• Astronomical factors: Changes in solar radiation, Earth’s orbit, and axial tilt.
• Atmospheric factors: Dust reflects heat; greenhouse gas levels are lower during glacial periods.

Red Tides and Eutrophication

A red tide is a type of harmful algal bloom caused by dinoflagellates. These blooms discolor water and release toxins harmful to marine life and humans.

Toxins bioaccumulate in predators and shellfish, leading to mass deaths and human illness. Airborne toxins can also cause beach closures and economic losses.

Salmon Farming and the ISA Virus

Fish farming reduces pressure on wild fish stocks. Freshwater fish like carp are grown in ponds, while saltwater fish such as salmon are raised in sea cages.

Advantages of Fish Farming

• Selective breeding for rapid growth
• Protection from predators
• Controlled feeding and water quality
• Reduced toxin exposure

A major threat to salmon farming is Infectious Salmon Anemia (ISA). While harmless to humans, it reduces fish health and yield.

Prevention of ISA

• Vaccination
• Disinfection of equipment
• Removal of infected fish

Female Reproductive System

The female reproductive system consists of the following organs:

Ovaries

The primary organs of the female reproductive system. Ovaries are composed of follicular cells, within which meiotic division occurs. This results in the maturation of a single ovum each month, which is released into the fallopian tubes for around 48 hours for possible fertilization.

Ovaries also secrete hormones such as estrogen and progesterone, which regulate the menstrual cycle.

Structurally, ovaries consist of an inner medulla (containing blood vessels and ligaments) and an outer cortex that houses ovarian follicles.

Within the ovaries, the ovarian cycle takes place.

The Ovarian Cycle

Each ovarian follicle contains a single immature egg (primary oocyte) surrounded by granulosa cells. These follicles have been suspended in early development since birth and are called primordial follicles.

Females are born with all the eggs they will ever have. Over time, follicles mature, but only one fully mature follicle ovulates per cycle. The rest undergo atresia.

The mature follicle responds to luteinizing hormone (LH) released by the pituitary gland. Rising estrogen levels create a positive feedback loop, triggering a surge of LH. Around day 14, the follicle ruptures and releases a mature ovum into the fallopian tube.

The ruptured follicle forms the corpus luteum, which secretes progesterone to thicken the endometrium. If fertilization does not occur, it degenerates into the corpus albicans, progesterone levels fall, and menstruation begins.

…Okay, back to the Female Reproductive System (holy yap)

Oviducts / Fallopian Tubes

These are 10–12 cm long tubes connecting the ovaries to the uterus. The ovum travels through them after ovulation.

The funnel-shaped infundibulum contains finger-like projections called fimbriae that sweep the ovum into the tube. This leads to the ampulla, then the isthmus, which connects to the uterus.

Uterus

A pear-shaped muscular organ with three layers:

• Perimetrium: outer layer
• Myometrium: muscular layer responsible for contractions during labour
• Endometrium: inner lining where implantation occurs

Vagina

The lower part of the birth canal, connected to the uterus via the cervix. It stretches during childbirth.

External Genitalia

• Labia majora & minora: folds protecting the vaginal opening
• Clitoris: sensitive structure analogous to the glans penis
• Mons pubis: fatty tissue over the pubic bone
• Hymen: thin membrane near the vaginal opening

The Mammary Glands

Cover your eyes, children! It’s a pair of boobies! (haha my humor is so mature)

Mammary glands are located in the breasts and are responsible for milk production through lactation, which nourishes newborns.

They exist as paired tissues surrounded by variable amounts of fat. Internally, they are composed of:

• Mammary alveoli: produce milk
• Mammary lobes: clusters of alveoli
• Mammary tubules: drain alveoli
• Mammary ducts: formed by merging tubules
• Ampullae: enlarged ducts that store milk
• Lactiferous ducts: deliver milk to the nipple

External structures include the nipples and areola.

The Menstrual Cycle

The menstrual cycle refers to the reproductive cycle that occurs in human females, repeating approximately every 28 days. The cycle consists of four main phases.

i. Menstruation (Bleeding Phase)

Duration: 3–7 days

Menstruation is the periodic discharge of blood, tissue, fluid, and mucus as the endometrium breaks down and is expelled through the vagina. This occurs when a mature ovum has been released but fertilization does not take place.

It is triggered by a drop in progesterone and estrogen levels. A similar hormonal drop during pregnancy would result in miscarriage due to collapse of the endometrial lining.

ii. Follicular Phase

Duration: Days 1–14

Rising levels of FSH and LH stimulate follicle development in the ovaries. Proliferation of follicular cells occurs via continuous cell division, while estrogen released by developing follicles promotes regeneration of the endometrium.

iii. Ovulation

Duration: 1 day (≈ Day 14)

A surge in LH causes the mature follicle to rupture, releasing the ovum from the ovary.

iv. Luteal (Secretory) Phase

The ruptured follicle becomes the corpus luteum, which secretes progesterone to maintain the endometrium. If fertilization does not occur, it degrades, hormone levels fall, and menstruation begins again.

Cell Division

Cell division is the process by which a parent cell divides into daughter cells. It occurs via mitosis (growth and repair) and meiosis (reproduction).

The Cell Cycle

The cell cycle lasts approximately 24 hours, with most of the time spent in interphase (G₀, G₁, S, and G₂), preparing the cell for division.

Mitosis

Mitosis produces two genetically identical diploid daughter cells and is essential for growth and tissue repair.

1. Prophase

Chromatin condenses into visible chromosomes. Centrosomes migrate to opposite poles and spindle fibres begin to form.

2. Prometaphase

The nuclear membrane and nucleolus disappear. Kinetochores form at centromeres, allowing spindle fibres to attach and begin aligning chromosomes toward the metaphase plate.

3. Metaphase

Chromosomes align precisely along the metaphase plate. The spindle checkpoint ensures all kinetochores are properly attached before progression.

4. Anaphase

Sister chromatids separate at the centromeres and are pulled toward opposite poles of the cell by shortening spindle fibres.

5. Telophase

Chromosomes decondense back into chromatin. Nuclear membranes reform, and the spindle apparatus disassembles.

Cytokinesis

The cytoplasm divides to form two identical daughter cells. Animal cells form a cleavage furrow, while plant cells form a cell plate.

History of DNA

Deoxyribonucleic acid (DNA) is the molecule responsible for storing genetic information. Cells use DNA to manufacture proteins such as enzymes and hormones.

• Friedrich Miescher: First isolated material from the nucleus of white blood cells, which he called nuclein.
• Phoebus Levene: Identified the three components of a nucleotide: deoxyribose sugar, phosphate group, and nitrogenous base.
• Erwin Chargaff: Discovered that the number of purines always equals the number of pyrimidines (A = T, G = C).
• Frederick Griffith: Demonstrated bacterial transformation while studying Streptococcus pneumoniae.
• Oswald Avery, Colin MacLeod, and Maclyn McCarty: Proved that DNA is the genetic material.
• Alfred Hershey and Martha Chase: Confirmed DNA as genetic material using bacteriophages.
• Linus Pauling: Proposed an incorrect triple-helix model of DNA.
• James Watson and Francis Crick: Proposed the double-helix model, but relied heavily on unpublished data and initially mispositioned the bases.

X-ray Crystallography and Photo 51

Maurice Wilkins and Rosalind Franklin used X-ray crystallography to study DNA. This technique involves firing X-rays through crystallized DNA fibers and analyzing the diffraction pattern.

Franklin’s famous image, Photo 51, provided clear evidence of DNA’s double-helix structure. Her data was shared without consent and used by Watson and Crick to finalize their model.

Structure of DNA

• DNA has a double-helix structure.
• It consists of a sugar-phosphate backbone.
• Nitrogenous bases pair via hydrogen bonds.
• Sugars and phosphates are linked by phosphodiester bonds.
• A–T form two hydrogen bonds; G–C form three.
• DNA is antiparallel.

In an antiparallel arrangement, one strand runs 5’ → 3’ while the complementary strand runs 3’ → 5’. This orientation is essential for DNA replication.

Topoisomerase prevents supercoiling of DNA during replication. As helicase unwinds the double helix, tension builds ahead of the replication fork, which may cause DNA to become tightly compacted. Topoisomerase relieves this strain by cutting, swiveling, and rejoining the DNA strands.

Single-stranded binding (SSB) proteins then bind to the separated strands, preventing them from re-annealing into a double helix.

Finally, the enzyme primase synthesizes short RNA primers on both strands. These primers provide a starting point for DNA polymerase.

This completes the initiation stage of DNA replication.

#2: Elongation

DNA polymerase synthesizes complementary nucleotides using the original strands as templates. However, DNA polymerase can only synthesize DNA in the 5’ → 3’ direction.

Because DNA strands are antiparallel, replication occurs differently on each strand:

DNA ligase joins Okazaki fragments together on the lagging strand, forming a continuous DNA strand.

#3: Termination

Replication ends when replication forks meet or reach the end of the DNA molecule. The result is two identical DNA molecules, each composed of one original strand and one newly synthesized strand.

Central Dogma of the Cell

The central dogma describes the flow of genetic information:

DNA → RNA → Protein

• DNA replicates to store genetic information.
• DNA is transcribed into mRNA.
• mRNA is translated by ribosomes to form proteins.
• Reverse transcription converts RNA back into DNA (used by some viruses).

Unit 3: Biotechnology

• Genetic modification and genetic engineering tools
• Production of insulin using GM technology
• Cloning: plant tissue culture and animal cloning
• Nuclear transfer
• Ethical implications of biotechnology
• GM crops and genetically modified organisms (GMOs)
• Human Genome Project: genome mapping and applications
• Ethics of stem cell research
• 3D tissue and organ bioprinting
• Treatment of genetic diseases using biotechnology

Unit 4: Interactions Between Organisms

Content:

• Species, habitat, ecosystem, and interdependence
• Energy transfer and trophic levels
• Pyramids of energy
• Food chains and food webs
• Biogeochemical cycles: carbon, nitrogen, phosphorus
• Ecological interactions: mutualism, parasitism, competition, predation
• Keystone species
• Population growth and factors affecting exponential growth
• Speciation and extinction
• Five-kingdom classification

Species, Habitat, Ecosystem & Interdependence

1. Species

Definition

A species is a group of organisms that share similar characteristics and are able to interbreed to produce fertile offspring. This means their offspring can also reproduce.

Key Characteristics of a Species

• Similar physical features (morphology)
• Same genetic makeup (DNA similarities)
• Ability to reproduce naturally with each other
• Produce fertile offspring

Examples

• Homo sapiens – humans
• Canis lupus familiaris – domestic dogs
• Panthera tigris – tigers
• Felis catus – domestic cats

Scientific Naming (Binomial Nomenclature)

Species are named using a two-part scientific system:

• Genus – first word, capitalized
• Species – second word, lowercase

Example: Homo sapiens

Importance of Species

• Maintains biodiversity
• Each species plays a role in its ecosystem
• Provides food, medicine, and ecosystem services
• Stabilizes food webs

2. Habitat

Definition

A habitat is the natural environment where an organism lives. It provides all the basic needs required for survival.

Basic Needs Provided by a Habitat

• Food
• Water
• Shelter
• Space
• Protection from predators
• Suitable temperature

Types of Habitats

Terrestrial (Land) Habitats

• Forests
• Grasslands
• Deserts
• Tundra
• Mountains

Aquatic (Water) Habitats

• Oceans
• Rivers
• Lakes
• Ponds
• Wetlands

Microhabitats

Small specific areas within a habitat that provide unique conditions.

• Under a rock
• Inside tree bark
• Leaf litter on forest floor

Adaptations to Habitat

Organisms have adaptations that help them survive in their habitat.

• Structural: thick fur, webbed feet
• Behavioral: migration, nocturnal activity
• Physiological: water conservation, temperature regulation

3. Ecosystem

Definition

An ecosystem is a community of living organisms (biotic factors) interacting with the non-living environment (abiotic factors).

Components of an Ecosystem

Biotic Factors (Living)

• Plants
• Animals
• Fungi
• Bacteria

Abiotic Factors (Non-living)

• Sunlight
• Temperature
• Water
• Soil
• Air
• Minerals

Types of Ecosystems

• Forest ecosystem
• Desert ecosystem
• Marine ecosystem
• Freshwater ecosystem
• Grassland ecosystem

Levels of Organization

1. Organism – one individual
2. Population – same species in one area
3. Community – different species in one area
4. Ecosystem – community + abiotic factors
5. Biosphere – all ecosystems on Earth

Energy Flow

Energy flows through ecosystems in a one-way direction.

• Sun → Producers → Consumers → Decomposers

Trophic Levels

• Producers: plants, algae
• Primary consumers: herbivores
• Secondary consumers: carnivores
• Tertiary consumers: top predators
• Decomposers: bacteria, fungi

4. Interdependence

Definition

Interdependence is the way organisms depend on each other for survival.

Why Interdependence is Important

• Maintains balance in ecosystems
• Ensures energy flow
• Controls population sizes
• Supports biodiversity

Types of Relationships

1. Mutualism (+ / +)

Both organisms benefit.

• Bees and flowers
• Birds removing parasites from animals

2. Commensalism (+ / 0)

One benefits, other unaffected.

• Remora fish and sharks
• Birds nesting in trees

3. Parasitism (+ / -)

One benefits, other harmed.

• Ticks on dogs
• Tapeworms in humans

4. Predation

One organism hunts and eats another.

• Lion and zebra
• Snake and mouse

5. Competition

Organisms compete for limited resources.

• Food
• Water
• Space
• Mates

5. Food Chains & Food Webs

Food chains and food webs show how energy and nutrients move through an ecosystem. They help scientists understand feeding relationships and ecosystem stability.

Food Chain

A food chain is a simple, linear sequence that shows who eats whom in an ecosystem. It always begins with a producer and ends with a top predator.

Structure of a Food Chain

1. Producer – makes its own food using photosynthesis (plants, algae)
2. Primary consumer – herbivore that eats plants
3. Secondary consumer – carnivore/omnivore
4. Tertiary consumer – top predator

Example Food Chain

Grass → Deer → Lion

This shows:

• Grass is the producer
• Deer is the primary consumer
• Lion is the secondary consumer

More Examples

• Phytoplankton → Fish → Shark
• Leaves → Caterpillar → Bird → Hawk

Energy Transfer

Only about 10% of energy is passed to the next trophic level. The rest is lost as:

• Heat
• Movement
• Respiration
• Waste

This explains why:

• Food chains are short
• There are fewer predators than prey

Food Web

A food web is a complex network of interconnected food chains. It shows all feeding relationships within an ecosystem.

Key Features

• One organism can have multiple food sources
• One organism can have multiple predators
• More realistic than food chains

Example

A rabbit may eat:

• Grass
• Leaves
• Seeds

A rabbit may be eaten by:

• Fox
• Eagle
• Snake

Decomposers in Food Webs

Decomposers play a vital role by breaking down dead organisms and waste.

• Bacteria
• Fungi

They:

• Recycle nutrients
• Return minerals to soil
• Support plant growth

Why Food Webs Are More Accurate

• Organisms eat more than one type of food
• Shows the complexity of ecosystems
• Represents real feeding behavior
• Helps predict the effects of population changes

Stability of Food Webs

Food webs are more stable because:

• If one species declines, others can replace it as food
• Energy has multiple pathways
• Ecosystems can recover more easily

Impact of Removing One Species

If one organism disappears:

• Predators may lose a food source
• Prey populations may increase
• Ecosystem balance is disrupted

Ecological Pyramids

Pyramid of Energy

Shows energy at each trophic level.

Pyramid of Biomass

Shows total mass of organisms.

Pyramid of Numbers

Shows population size.

All pyramids:

• Get smaller at the top
• Show energy loss

6. Human Impact

Human activities significantly affect ecosystems, species, and natural processes. These impacts can be negative, causing environmental damage, or positive, helping to restore and protect nature.

Negative Impacts

1. Deforestation

Deforestation is the large-scale removal of trees from forests. It is mainly caused by:

• Agriculture (clearing land for crops and livestock)
• Urban development (building cities, roads, infrastructure)
• Logging for timber and paper products

Consequences:

• Loss of habitat for forest species
• Decrease in biodiversity
• Increased carbon dioxide levels (less trees to absorb CO₂)
• Soil erosion and landslides
• Disruption of the water cycle

2. Pollution

Pollution occurs when harmful substances are released into the environment.

Types of Pollution

• Air pollution: vehicle exhaust, factory smoke
• Water pollution: sewage, oil spills, chemicals
• Soil pollution: pesticides, landfill waste
• Noise pollution: traffic, construction

Effects:

• Health problems in humans and animals
• Death of aquatic organisms
• Bioaccumulation of toxins in food chains
• Acid rain damaging plants and buildings

3. Climate Change

Climate change refers to long-term changes in global temperature and weather patterns. It is mainly caused by the greenhouse effect.

Main causes:

• Burning fossil fuels (coal, oil, gas)
• Deforestation
• Industrial emissions

Impacts:

• Rising global temperatures
• Melting glaciers and polar ice
• Sea level rise
• More extreme weather (heatwaves, floods, hurricanes)
• Coral bleaching
• Species extinction

4. Overfishing

Overfishing occurs when fish are caught faster than they can reproduce.

Causes:

• Commercial fishing
• Use of large fishing nets
• Illegal fishing practices

Consequences:

• Decline in fish populations
• Disruption of marine food webs
• Threat to food security
• Bycatch (unwanted species caught)

5. Habitat Destruction

Habitat destruction occurs when natural environments are damaged or completely removed.

Main causes:

• Mining
• Dam construction
• Urbanization
• Road building

Effects:

• Species forced to migrate
• Population decline
• Extinction
• Fragmentation of habitats

Positive Actions

1. Conservation

Conservation is the protection and careful management of natural resources.

• Protecting endangered species
• Managing ecosystems sustainably
• Breeding programs in zoos
• Community education

2. Reforestation

Reforestation is planting trees in areas where forests were cut down.

• Restores habitats
• Absorbs carbon dioxide
• Prevents soil erosion
• Improves air quality

3. Protected Areas

Protected areas are regions where human activities are limited.

• National parks
• Wildlife reserves
• Marine sanctuaries

Purpose:

• Protect biodiversity
• Allow ecosystems to recover
• Support scientific research

4. Sustainable Farming

Sustainable farming reduces environmental damage while producing food.

• Crop rotation
• Organic fertilizers
• Water conservation
• Reduced pesticide use

Benefits:

• Maintains soil fertility
• Protects pollinators
• Reduces pollution

5. Reducing Waste

Reducing waste helps decrease pollution and conserve resources.

• Recycling
• Reusing materials
• Composting organic waste
• Avoiding single-use plastics

Impact:

• Less landfill waste
• Reduced ocean pollution
• Lower greenhouse gas emissions

Energy Transfer & Trophic Levels

Energy transfer explains how energy moves through an ecosystem, while trophic levels describe the different feeding positions organisms occupy in a food chain or food web. Together, they help scientists understand ecosystem structure, population size, and stability.

1. Source of Energy in Ecosystems

The Sun is the primary source of energy for almost all ecosystems on Earth. Plants capture sunlight through photosynthesis.

Photosynthesis equation:

Carbon dioxide + Water → Glucose + Oxygen (using sunlight)

This process:

• Converts light energy into chemical energy
• Stores energy in glucose molecules
• Forms the base of all food chains

2. Energy Transfer

Energy transfer refers to the movement of energy from one organism to another through feeding relationships.

How Energy Moves

Energy moves in a one-way direction:

Sun → Producers → Consumers → Decomposers

• Energy is NOT recycled
• It is eventually lost as heat

The 10% Rule

Only about 10% of energy is passed to the next trophic level. The remaining 90% is lost due to:

• Respiration
• Movement
• Heat loss
• Waste production

This explains:

• Why food chains are short
• Why top predators are few in number

3. Trophic Levels

A trophic level is a feeding position in a food chain or food web.

Major Trophic Levels

• Level 1 – Producers
• Level 2 – Primary consumers
• Level 3 – Secondary consumers
• Level 4 – Tertiary consumers

Level 1: Producers (Autotrophs)

Producers make their own food using:

• Photosynthesis (plants, algae)
• Chemosynthesis (deep-sea bacteria)

Importance:

• Form the base of all food chains
• Provide energy to all consumers
• Release oxygen

Level 2: Primary Consumers

Primary consumers are herbivores that feed directly on producers such as plants and algae. They occupy the second trophic level in a food chain.

Their role in the ecosystem is very important because:

• They transfer energy from plants to higher trophic levels
• They control plant population growth
• They form the main food source for predators

Primary consumers have special adaptations:

• Flat teeth for grinding plants
• Long digestive systems to break down cellulose
• Some have symbiotic bacteria to digest plant material

Examples:

• Deer – grazes on grass and leaves in forests
• Rabbit – eats grass and vegetables in meadows
• Caterpillar – feeds on plant leaves

If primary consumers disappear:

• Plant populations increase uncontrollably
• Secondary consumers lose their food source
• The food chain collapses

Level 3: Secondary Consumers

Secondary consumers feed on primary consumers. They are usually carnivores or omnivores.

They occupy the third trophic level in a food chain.

Their ecological role:

• Control herbivore populations
• Prevent overgrazing of plants
• Maintain ecosystem balance

Adaptations of secondary consumers:

• Sharp teeth and claws for hunting
• Strong jaws to catch prey
• Good eyesight and speed

Examples:

• Snake – eats rodents and frogs
• Frog – eats insects and small animals
• Fox – hunts rabbits and birds

If secondary consumers disappear:

• Herbivore populations increase rapidly
• Plants become overgrazed
• The ecosystem becomes unstable

Level 4: Tertiary Consumers

Tertiary consumers are top predators that occupy the highest trophic level in a food chain or food web. They feed on secondary consumers and have no natural predators in their ecosystem.

Because of energy loss at each trophic level:

• Tertiary consumers are few in number
• They require large territories
• They need to eat many prey organisms to survive

This makes them:

• Highly vulnerable to extinction
• Strong indicators of ecosystem health
• Important regulators of population sizes

Examples:

• Lion – controls herbivore populations in savanna ecosystems
• Hawk – controls rodent and small bird populations
• Shark – maintains balance in marine food webs

If tertiary consumers disappear:

• Secondary consumer populations increase
• Herbivore numbers rise
• Producers become overgrazed
• The ecosystem becomes unstable

4. Decomposers

Decomposers are organisms that break down dead plants, dead animals, and organic waste into simpler substances.

They are essential because they prevent:

• Build-up of dead organisms
• Waste accumulation
• Nutrient loss from ecosystems

Examples:

• Bacteria – microscopic organisms that chemically break down matter
• Fungi – release enzymes to digest dead material externally

How Decomposers Work

Decomposers:

• Secrete digestive enzymes
• Break complex molecules into simple nutrients
• Absorb these nutrients

Their Role in Ecosystems

• Recycle nutrients – nitrogen, phosphorus, carbon
• Return minerals to soil – improves soil fertility
• Support plant growth – plants reuse nutrients

This creates a nutrient cycle:

Plants → Animals → Decomposers → Soil → Plants

Energy vs Nutrient Cycling

Unlike energy:

• Energy flows in one direction and is lost as heat
• Nutrients are recycled continuously

This is important because:

• Ecosystems would collapse without nutrient recycling
• Plants would run out of essential minerals
• Food chains would stop functioning

5. Ecological Pyramids

Pyramid of Energy

Shows energy at each trophic level.

• Always upright
• Largest at producer level
• Smallest at top predator level

Pyramid of Biomass

Shows total mass of organisms.

Pyramid of Numbers

Shows number of organisms.

6. Why Energy Transfer is Inefficient

Energy transfer between trophic levels is inefficient because only a small fraction of energy is passed on to the next level. Most energy is lost to the environment or used by organisms for survival.

1. Not All Food Is Eaten

Organisms do not consume every part of the organism they feed on.

Examples:

• Predators may leave bones, fur, feathers, or shells
• Herbivores may not eat roots or tough stems

Because these parts are not eaten:

• The energy stored in them is not transferred
• It goes to decomposers instead

2. Some Food Is Indigestible

Even when food is eaten, organisms cannot digest all of it.

Examples:

• Cellulose in plant cell walls
• Chitin in insect exoskeletons
• Keratin in hair and feathers

This undigested material:

• Leaves the body as feces
• Contains stored energy
• Is unavailable to the next trophic level

3. Energy Lost as Heat

Organisms use energy for respiration.

During respiration:

• Glucose is broken down
• Energy is released
• Much of it is lost as heat

This heat:

• Maintains body temperature
• Escapes into the environment
• Cannot be reused by other organisms

4. Energy Used for Life Processes

Energy is constantly needed for survival.

Life processes include:

• Movement (running, flying, swimming)
• Growth and repair of cells
• Reproduction
• Maintaining internal balance (homeostasis)

Because energy is used for these processes:

• It is not stored as biomass
• It cannot be passed to the next trophic level

Overall Summary

Due to all the energy losses that occur at each trophic level, energy transfer in ecosystems is highly inefficient. This means that:

• Only about 10% of the energy stored in one trophic level is passed on to the next level.
• The remaining 90% of energy is lost through:
  • Heat from respiration
  • Movement and activity
  • Undigested food
  • Waste products

Because so much energy is lost:

• Food chains are usually short and rarely exceed four or five trophic levels.
• There is less energy available to support organisms at higher levels.
• This explains why top predators (such as lions, eagles, and sharks) are:
  • Few in number
  • Spread over large territories
  • More vulnerable to extinction

Understanding this inefficiency is extremely important because it:

• Controls population sizes – there are many producers, fewer herbivores, and very few carnivores.
• Maintains ecosystem balance – prevents overpopulation of any single species.
• Shapes food web structure – determines how many organisms an ecosystem can support at each level.
• Helps scientists predict the impact of disturbances such as habitat loss or species extinction.

In conclusion, energy transfer inefficiency is not a weakness of ecosystems, but a natural process that regulates life and ensures long-term stability and sustainability.

Effect of Producer Decline (continued)

• Herbivores lose their main food source and their populations decrease
• Carnivores then lose prey and their populations also decrease
• This creates a trophic cascade – a chain reaction that affects every level of the ecosystem

Eventually, this can lead to:

• Species extinction
• Collapse of food webs
• Loss of biodiversity

Impact on Ecosystem Stability

Ecosystems remain stable when:

• Energy flows efficiently from producers to consumers
• Populations are balanced
• No species dominates excessively

However, when energy flow is disrupted:

• Some species overpopulate
• Others decline rapidly
• Natural balance is lost

This instability can cause:

• Soil degradation
• Reduced plant growth
• Loss of pollinators
• Lower food availability

Real-Life Example: Forest Ecosystem

In a forest:

• Trees and plants are the producers
• Deer and insects are primary consumers
• Wolves and big cats are secondary consumers

If deforestation occurs:

• Producer numbers decrease
• Herbivores lose food and shelter
• Predator populations crash

This shows how:

• Energy loss multiplies the damage
• Entire ecosystems can collapse

Why This Matters

Understanding the impact of energy loss helps us:

• Protect endangered species
• Manage ecosystems sustainably
• Prevent ecosystem collapse
• Predict effects of climate change

In conclusion, energy loss controls:

• How many organisms an ecosystem can support
• Which species survive
• How stable the ecosystem remains

This proves that energy flow is the backbone of ecosystem structure.

1. Species, Habitat, Ecosystem & Interdependence

1.1 Species

A species is a group of organisms that:

• Have similar physical and genetic characteristics
• Can interbreed naturally
• Produce fertile offspring

This means:

• They share a common gene pool
• They are reproductively compatible
• They cannot successfully breed with other species

Examples:

• Humans – Homo sapiens
• Dogs – Canis lupus familiaris
• Tigers – Panthera tigris

Each species has:

• Specific adaptations
• Unique behaviors
• Special survival strategies

These adaptations help species:

• Find food
• Avoid predators
• Reproduce successfully
• Survive in their environment

1.2 Habitat

A habitat is the natural home or environment where an organism lives. It is the place that provides all the resources needed for survival.

Every habitat must supply:

• Food – energy for growth, movement, and reproduction
• Water – essential for chemical reactions and life processes
• Shelter – protection from predators and harsh weather
• Space – enough area to find resources and mates
• Suitable climate – correct temperature and rainfall

Each species is specially adapted to its habitat. These adaptations can be:

• Structural (body shape, fur, leaves)
• Behavioral (migration, hunting patterns)
• Physiological (water storage, temperature control)

Types of Habitats

Habitats are classified into two main groups:

• Terrestrial habitats – found on land
• Aquatic habitats – found in water

1. Terrestrial Habitats (Land)

These habitats occur on land and vary based on climate and vegetation.

• Forest
  • High rainfall
  • Dense trees and plants
  • Examples: rainforest, deciduous forest
  • Species: monkeys, birds, insects
• Grassland
  • Moderate rainfall
  • Grasses dominate
  • Few trees
  • Species: zebras, lions, antelope
• Desert
  • Very low rainfall
  • Extreme temperatures
  • Plants store water (cactus)
  • Species: camels, snakes, lizards
• Tundra
  • Extremely cold
  • Frozen soil (permafrost)
  • Short growing season
  • Species: polar bears, arctic fox
• Mountain
  • Low oxygen levels
  • Cold climate
  • Species: snow leopards, yaks

2. Aquatic Habitats (Water)

These habitats occur in water and are divided into:

• Freshwater
• Marine

• Freshwater habitats
  • Rivers
  • Lakes
  • Ponds
  • Wetlands
  • Species: frogs, fish, insects
• Marine habitats
  • Oceans
  • Coral reefs
  • Estuaries
  • Species: sharks, whales, coral

Importance of Habitat

Habitats are essential because they:

• Support food chains
• Maintain biodiversity
• Provide breeding sites
• Allow species to survive

If a habitat is destroyed:

• Organisms lose food and shelter
• Populations decrease
• Species may become extinct

Human Impact on Habitats

Humans damage habitats through:

• Deforestation
• Urbanization
• Pollution
• Climate change

To protect habitats, humans:

• Create protected areas
• Restore ecosystems
• Reduce pollution

Summary

• A habitat is an organism’s natural home
• It provides all survival needs
• Different habitats support different species
• Organisms are adapted to their habitats

This proves that habitats are critical for survival and ecosystem balance.

Every species is adapted to its specific habitat.

Examples of Adaptations

Habitats can be:

• Terrestrial (land)
• Aquatic (water)

Some known habitats:

• Forest
• Grassland
• Desert
• Ocean
• Freshwater lakes
• Tundra

If a habitat changes:

• Species may struggle to survive
• Populations may decline
• Extinction may occur

1.3 Ecosystem

An ecosystem is a community of:

• Living organisms (biotic factors)
• Non-living components (abiotic factors)

These interact with each other in a specific area.

Biotic Factors

• Plants
• Animals
• Bacteria
• Fungi

Basically living things

Abiotic Factors

• Sunlight
• Temperature
• Water
• Soil
• Oxygen
• Minerals

Just non-living things.

Ecosystems can be:

• Small (pond, garden)
• Large (forest, ocean, desert)

Examples:

• Coral reef ecosystem
• Rainforest ecosystem
• Grassland ecosystem

Within an ecosystem:

• Energy flows
• Nutrients cycle
• Organisms depend on each other

1.4 Interdependence

Interdependence means organisms depend on each other for survival.

No organism survives alone.

Living things depend on:

• Other organisms
• The environment

Examples of Interdependence

• Plants depend on animals for pollination
• Herbivores depend on plants for food
• Carnivores depend on herbivores
• Decomposers depend on dead organisms

Types of interdependence:

• Food relationships
• Habitat sharing
• Symbiotic relationships

Food Interdependence

Energy flows through:

• Producers
• Consumers
• Decomposers

If one species disappears:

• Food chains are disrupted
• Populations become unbalanced
• Other species may go extinct

1.5 Real-Life Example

Forest ecosystem:

• Trees – producers
• Deer – herbivores
• Wolves – carnivores
• Fungi – decomposers

Interdependence:

• Deer eat plants
• Wolves eat deer
• Dead organisms are decomposed
• Nutrients return to soil
• Plants grow again

This forms a:

• Balanced ecosystem
• Continuous cycle

1.6 Importance of Interdependence

Interdependence:

• Maintains ecosystem balance
• Controls population sizes
• Ensures energy flow
• Prevents overpopulation

If interdependence is disturbed:

• Food webs collapse
• Species decline
• Biodiversity decreases

1.7 Summary

• A species is a group that can reproduce
• A habitat is where organisms live
• An ecosystem includes living and non-living factors
• Interdependence links all organisms

Biogeochemical Cycles: Carbon, Nitrogen, Phosphorus

Biogeochemical Cycles Overview

Biogeochemical cycles are the natural pathways through which essential chemical elements and compounds move between living organisms (biotic factors) and the environment (abiotic factors). These cycles ensure that vital elements are recycled continuously, making them available for life processes such as growth, reproduction, and energy transfer.

The most important cycles include the carbon cycle, the nitrogen cycle, and the phosphorus cycle. Each cycle operates differently depending on the element’s chemical properties but all are essential to maintaining ecosystem balance and supporting life.

Carbon Cycle

Carbon is a key component of all living matter because it forms the backbone of organic molecules such as carbohydrates, proteins, fats, and nucleic acids. Carbon cycles between the atmosphere, living organisms, soils, oceans, and fossil fuels.

Key Processes:

• Photosynthesis: Plants, algae, and some bacteria absorb carbon dioxide (CO₂) from the atmosphere and convert it into glucose, storing energy in chemical bonds.
• Respiration: Organisms release CO₂ back into the atmosphere by breaking down glucose for energy.
• Decomposition: Decomposers such as bacteria and fungi break down dead organisms, returning carbon to the soil and atmosphere.
• Combustion: Burning of fossil fuels and biomass releases stored carbon as CO₂ into the atmosphere, increasing greenhouse gas levels.
• Ocean Uptake: Oceans absorb CO₂, which is stored as dissolved carbon or used by marine organisms to make shells and skeletons.

Importance: The carbon cycle regulates atmospheric CO₂ levels, supports plant growth, and influences global climate. Disruptions to this cycle, such as excessive CO₂ from fossil fuel burning, can cause global warming and ecosystem imbalance.

Nitrogen Cycle

Nitrogen is an essential element for building proteins, nucleic acids, and other biomolecules. Although N₂ gas makes up about 78% of the atmosphere, most organisms cannot use it directly.

Key Processes:

• Nitrogen Fixation: Nitrogen-fixing bacteria in soil or root nodules convert atmospheric N₂ into ammonium (NH₄⁺), which plants can absorb. Lightning also converts N₂ into usable forms.
• Nitrification: Nitrifying bacteria convert ammonium into nitrites (NO₂^-) and then nitrates (NO₃^-), which are readily absorbed by plants.
• Assimilation: Plants use nitrates to synthesize proteins and nucleic acids. Animals obtain nitrogen by eating plants or other animals.
• Ammonification: Decomposers break down organic nitrogen from dead organisms and waste, returning ammonium to the soil.
• Denitrification: Denitrifying bacteria convert nitrates back into N₂ gas, returning nitrogen to the atmosphere and completing the cycle.

Importance: The nitrogen cycle provides usable nitrogen to all living organisms, supports protein and DNA synthesis, and maintains soil fertility. Human activities, such as excessive fertilizer use, can disrupt this cycle and lead to water pollution and algal blooms.

Phosphorus Cycle

Phosphorus is essential for ATP (energy transfer), nucleic acids (DNA and RNA), and cell membranes. Unlike carbon and nitrogen, phosphorus does not exist as a gas in the atmosphere; it primarily cycles through rocks, soil, water, and living organisms.

Key Processes:

• Weathering: Rocks release phosphate ions (PO₄^3-) into soil and water.
• Absorption: Plants absorb phosphate ions from the soil for growth.
• Consumption: Animals obtain phosphorus by eating plants or other animals.
• Decomposition: Decomposers return phosphorus to the soil from dead organisms and waste products.
• Runoff and Sedimentation: Phosphates can enter rivers and oceans, where they may accumulate in sediments, eventually forming new rocks over geological time.

Importance: Phosphorus is vital for energy transfer (ATP), genetic material, and healthy plant growth. Human activities such as mining and fertilizer use can cause phosphorus pollution, leading to eutrophication in aquatic ecosystems.

Human Impacts on Biogeochemical Cycles

Humans can significantly disrupt these cycles:

• Carbon: Burning fossil fuels and deforestation increase atmospheric CO₂, contributing to global warming.
• Nitrogen: Excessive use of fertilizers leads to nitrogen runoff, causing eutrophication and oxygen depletion in water bodies.
• Phosphorus: Mining and agricultural runoff add phosphates to rivers and lakes, triggering algal blooms and ecosystem imbalance.

Maintaining the balance of these cycles is essential for sustainable ecosystems, biodiversity, and life on Earth.

Ecological Interactions: Mutualism, Parasitism, Competition, Predation

Overview of Ecological Interactions

Ecological interactions describe the relationships between organisms within an ecosystem. These interactions influence survival, reproduction, population dynamics, and the overall stability of ecosystems. Interactions can be interspecific (between different species) or intraspecific (within the same species). Understanding these interactions is crucial to predict ecosystem responses to changes such as habitat loss, species introduction, or climate change.

Mutualism

Mutualism is a type of interaction where both species benefit from the relationship. This is a positive-positive (+/+) interaction. Mutualism can be obligate (species cannot survive without each other) or facultative (species benefit but can survive independently).

Examples and Adaptations

• Bees and flowers: Bees collect nectar for food, while flowers benefit from pollination. Adaptations: flowers have bright colors, scent, and nectar; bees have specialized mouthparts and vision for detecting flowers.
• Clownfish and sea anemone: Clownfish get protection from predators, anemones get cleaned and receive nutrients from fish waste. Adaptations: mucus coating on clownfish prevents stings; anemone tentacles provide shelter.
• Gut bacteria and humans: Bacteria receive nutrients and shelter; humans benefit from digestion of complex carbohydrates and vitamin production. Adaptations: bacteria adapted to anaerobic conditions; humans have specific gut niches.

Ecological Significance:

• Enhances biodiversity by supporting multiple species simultaneously.
• Increases ecosystem productivity.
• Stabilizes population sizes through interdependence.

Parasitism

Parasitism is an interaction where one organism benefits (the parasite) while the other is harmed (the host). This is a positive-negative (+/–) relationship. Parasites may be ectoparasites (external) or endoparasites (internal).

Examples and Adaptations

• Tape worms in mammals: Parasite absorbs nutrients inside the host's intestine. Adaptations: hooks and suckers for attachment; thin body for nutrient absorption.
• Fleas on dogs: Suck blood and may transmit diseases. Adaptations: strong legs for jumping, specialized mouthparts, flattened body for moving through fur.
• Mistletoe on trees: Extracts water and minerals from host plant. Adaptations: haustoria penetrate host tissues; seeds stick to branches for dispersal.

Ecological Significance:

• Controls host population size and distribution.
• Can influence food web dynamics by weakening hosts.
• Drives co-evolution; hosts develop defense mechanisms while parasites evolve counter-adaptations.

Competition

Competition occurs when organisms compete for the same limited resources, such as food, space, or mates. It can be intraspecific (within a species) or interspecific (between species). This interaction is negative-negative (–/–) because both parties may lose resources or expend energy.

Examples and Adaptations

• Plants competing for sunlight: Taller plants overshadow shorter ones. Adaptations: rapid vertical growth, broad leaves, shade tolerance.
• Lions and hyenas competing for prey: Both species hunt or scavenge the same animals. Adaptations: lions develop strength and teamwork; hyenas have stamina and cooperative hunting.
• Intraspecific competition in deer: Males compete for mates during the rutting season. Adaptations: antler size, fighting strategies, territorial marking.

Ecological Significance:

• Determines population size and distribution.
• Drives natural selection; organisms evolve adaptations to reduce competition.
• Promotes niche differentiation, allowing species to coexist in the same habitat.

Predation

Predation occurs when one organism (predator) kills and eats another (prey). This is a positive-negative (+/–) interaction. Predators influence prey populations, while prey develop defensive adaptations.

Examples and Adaptations

• Lions and zebras: Lions hunt zebras for food. Adaptations: lions have speed, strength, and teamwork; zebras have running speed, herd vigilance, and camouflage stripes.
• Owls and mice: Owls hunt small nocturnal mammals. Adaptations: silent flight, acute night vision (owl); burrowing, nocturnal activity (mice).
• Praying mantis and insects: Mantises ambush smaller insects. Adaptations: camouflage, rapid forelimb strikes for capture.

Ecological Significance:

• Regulates prey population and prevents overgrazing or overpopulation.
• Maintains ecosystem balance and food web stability.
• Drives co-evolution; predators evolve hunting strategies, prey evolve defense mechanisms.

Summary of Ecological Interactions

Understanding these interactions is critical for studying ecosystems because they determine population dynamics, energy flow, and the structure of communities. Human activities such as habitat destruction, species introduction, and overexploitation can disrupt these interactions, leading to ecosystem instability.

Keystone Species

Overview

A keystone species is a species that has a disproportionately large impact on its ecosystem relative to its abundance. Although keystone species may not be the most numerous or dominant in terms of biomass, they play a critical role in maintaining the structure, diversity, and function of the ecosystem.

The removal of a keystone species often triggers dramatic changes in the ecosystem, including population declines, altered food webs, and even local extinctions. They are considered essential for ecosystem stability and biodiversity.

Types of Keystone Species

• Predators: Control populations of prey species, preventing overgrazing or overpopulation. Example: Sea otters in kelp forests keep sea urchin populations in check, allowing kelp to thrive.
• Mutualists: Provide critical services to other species, such as pollination or seed dispersal. Example: Hummingbirds or certain bees pollinate plants that are essential for other species’ survival.
• Engineers (Ecosystem Modifiers): Modify the environment in ways that benefit many species. Example: Beavers build dams that create wetlands, supporting fish, birds, and amphibians.
• Foundational Species: Often primary producers that structure the ecosystem. Example: Kelp in kelp forests, corals in coral reefs.

Characteristics of Keystone Species

• Exert a large influence on community structure despite low abundance.
• Help maintain species diversity and population balance.
• Interact with multiple trophic levels in the food web.
• Often create or maintain habitats that support other organisms.
• Removal usually leads to cascading ecological effects (trophic cascades).

Examples of Keystone Species

Ecological Importance

• Maintain ecosystem diversity by controlling dominant species.
• Regulate population dynamics across trophic levels.
• Shape the physical environment (habitat formation).
• Influence food web stability and energy flow.
• Prevent ecological collapse by supporting complex interactions.

Human Impacts on Keystone Species

• Hunting, fishing, and overexploitation can remove keystone predators or mutualists.
• Habitat destruction reduces populations of ecosystem engineers like beavers or coral species.
• Introduction of invasive species may outcompete or prey upon keystone species.
• Pollution, climate change, and ocean acidification threaten foundational species such as coral and kelp.

Conservation of keystone species is critical to maintaining ecosystem health. Protecting them often has a multiplier effect, supporting the survival of many other species and preserving biodiversity.

Population Growth and Factors Affecting Exponential Growth

Population Growth Overview

Population growth describes the change in the number of individuals in a population over time. Understanding population dynamics is essential for ecology, conservation biology, and resource management. Populations grow due to births and immigration, and decrease due to deaths and emigration.

Types of Population Growth

• Exponential Growth (J-shaped curve): Occurs when resources are unlimited and environmental conditions are ideal. Population increases rapidly at a constant rate, doubling over regular intervals. Example: Bacterial growth in nutrient-rich media.
• Logistic Growth (S-shaped curve): Growth slows as population reaches the carrying capacity (K) of the environment due to limited resources, competition, predation, or disease. Example: Deer population in a forest stabilizing as food becomes limiting.

Factors Affecting Exponential Growth

Exponential growth is influenced by both biotic and abiotic factors:

Abiotic Factors

• Availability of resources: water, nutrients, and food.
• Temperature and climate conditions affecting survival and reproduction.
• Space for shelter, breeding, and movement.
• Environmental disturbances such as fires, floods, or pollution.

Biotic Factors

• Reproductive rate: high birth rates lead to faster growth.
• Predation pressure: fewer predators allow populations to increase faster.
• Disease and parasitism: epidemics reduce population size.
• Competition: intraspecific competition can limit growth by reducing resources per individual.

Carrying Capacity and Limiting Factors

Even populations that initially grow exponentially will eventually be limited by carrying capacity, which is the maximum number of individuals an ecosystem can sustain. Limiting factors can be:

• Density-dependent: competition, predation, disease (effects increase with population size)
• Density-independent: natural disasters, temperature extremes, habitat destruction (effects independent of population size)

Real-World Example

Rabbits introduced to Australia initially experienced exponential growth due to abundant food, few predators, and mild climate. Over time, limiting factors such as disease (myxomatosis) and competition slowed growth, stabilizing populations.

Speciation and Extinction

Speciation

Speciation is the process by which new species arise from existing ones. It is the foundation of biodiversity and occurs through genetic variation and natural selection over time. Speciation can be allopatric, sympatric, or parapatric.

Types of Speciation

• Allopatric Speciation: Occurs when populations are geographically separated. Genetic differences accumulate over time, resulting in reproductive isolation. Example: Darwin’s finches on the Galápagos Islands.
• Sympatric Speciation: Occurs without geographic isolation, often through behavioral or ecological differences within the same area. Example: Apple maggot flies feeding on different host plants in the same region.
• Parapatric Speciation: Occurs when populations are adjacent, with limited gene flow. Environmental gradients cause differentiation. Example: Grass species along heavy metal-contaminated soil gradients.

Mechanisms Driving Speciation

• Mutation: Introduces new genetic variants.
• Natural selection: Favors traits that improve survival or reproduction.
• Genetic drift: Random changes in allele frequencies, especially in small populations.
• Reproductive isolation: Prevents interbreeding between diverging populations.

Extinction

Extinction is the complete disappearance of a species from Earth. It can occur naturally or be accelerated by human activities. Extinction reduces biodiversity and can disrupt ecosystems.

Types of Extinction

• Background extinction: Natural rate of extinction over geological time.
• Mass extinction: Large-scale events where many species disappear in a short period (e.g., dinosaurs at the end of the Cretaceous).
• Anthropogenic extinction: Human-caused extinctions due to habitat destruction, overhunting, pollution, and climate change.

Causes of Extinction

• Habitat loss and fragmentation
• Introduction of invasive species
• Overexploitation (hunting, fishing, harvesting)
• Climate change altering ecosystems
• Disease outbreaks

Ecological Impacts of Extinction

• Loss of keystone species can trigger trophic cascades.
• Reduction in ecosystem productivity and resilience.
• Disruption of food webs and nutrient cycles.
• Decreased genetic diversity reduces adaptability of surviving species.

Real-World Example

The dodo (Raphus cucullatus) is a classic example of human-induced extinction. Hunting and introduced species (rats, pigs) led to the complete loss of this flightless bird from Mauritius, impacting seed dispersal of native plants.