bio unit 2 orgamisms and their environment 2026 y3

What do animals gain through consumption?

Consumers gain a source of energy (ATP from cellular respiration) and nutrients (biomolecules) from the food ingested. The energy is used to carry our cellular processes and the biomolecules are used to build new protoplasm/biomass of the consumers, resulting in growth.

Why are food chains short?

1. Energy transfer between tropic levels is inefficient, only about 10% (change % depending on question) of energy is transferred from one tropic level to another hence after the (last trophic level depending on qn), there is very little and insufficient energy remaining to sustain another trophic level of consumer population

2. Up a food chains, the biomass decreases also

Why are marine food chains longer than terrestrial food chains? Normally, how many trophic levels do Marine and terrestrial food chains have?

Most terrestrial food chains have 4 trophic levels while most marine food chains ave 6 trophic levels.

1. Abundant microscopic phytoplankton producers→higher base energy production

2. More efficient energy transfer from one trophic level to the next (20% efficiency)

What’s a pyramid of numbers and what are the conditions for pyramid to be inverted

A pyramid of numbers shows the number of organisms at each trophic level at a particular time. Pyramid MAY be inverted if consumer is parasitic, producer is a single but large organism (qty of producer is 1 so base is small)

Advantages and disadvantages of pyramid of numbers

Advantages:

1. Easy and fast data collection using sampling counts

2. Good for comparing changes in ecosystem at different times of the year/ different seasons

Disadvantages:

1. Numbers may be too large to measure accurately

2. Producers may vary in size and pyramid might be inverted if the consumer is parasitic (small but many in qty so large top) or producer is a single large organism (large in size, small in qty(1), so narrow base)

3. Does not take into account juvenile or immature forms

What’s a pyramid of biomass and how to determine?

A pyramid of biomass shows the total dry mass/standing mass of organisms at each trophic level at a particular time.

Anaesthetise the animal, then kill them, then dry them in an oven at 100°c until a constant mass is obtained to remove water. If qty is large, obtain dry mass of a few of the animals then multiply

What can cause an inverted pyramid of biomass?

Producer reproduces quickly, faster than rate of consumption by primary consumer

Advantages and disadvantages of pyramid of biomass

Advantages:

1. Eliminates problem of size differences

Disadvantages:

1. Data labor-intensive and costly to collect-involves killing the organism

2. Organisms of same mass may have different energy content

3. It is constructed at a particular point in time, not taking into account rate of reproduction or rate of consumption of organisms. Pyramid may be inverted if producer has high turnover rate(rate where the producer reproduces to replace dead kinda aka rate of reproduction)

Define nutrient cycle

Nutrient cycle is the movement of chemical nutrients in the environment: water, carbon, oxygen, nitrogen brought about by physical, chemical and biological processes

What happens if dont have nutrient cycle

Nutrients remain locked up in dead organisms, turning into fossil fuels over time.

Carbon cycle processes

1. Photosynthesis: plants absorb atmospheric carbon dioxide to manufacture carbohydrates (eg glucose). Some carbohydrates are converted to proteins and fats.

2. Feeding: When animals feed on plants or other animals, the digested carbon compounds become assimilated as part of their bodies

3. Respiration: Living organisms break down carbon compounds(eg glucose) to release CO2 into the atmosphere

4. Decomposition: decomposers like bacteria and fungi break down waste products into simple organic and inorganic substances including carbon dioxide

5. Formation of fossil fuels and combustion: Dead bodies of plants and animals buried deep into the earth are subjected to high pressure and temperature, converting them into fossil fuels such as coal, natural gas and oil. Combustion of fossil fuels release carbon dioxide into environment

Define a carbon sink and describe examples of natural and artificial carbon sinks

A carbon sink absorbs more carbon than is released.

Natural carbon sinks include forests, the ocean, soil. Artificial carbon sinks are landfills.

Describe forests as a carbon sink and how it acts as a carbon sink

Forests absorb about 1/5 of CO2 released by human activities

1. Trees capture atmospheric carbon dioxide and store large amounts of carbon dioxide as biomass in trunk, roots, leaf litter and soil,driven by photosynthesis

2. When trees die under anaerobic and acidic conditions, decomposition is incomplete. over time,large quantities of organic matter accumulates and compresses into a dark brown acidic substance called peat which is converted to FOSSIL FUELS under high temperatures and pressures

How do oceans act as large carbon sinks?

Oceans absorb about 1/3 of CO2 released by human activities through:

1. Dissolution: Carbon dioxide dissolves in sea water to form carbonic acid and is used by phytoplankton and algae in photosynthesis

2. Many marine organisms eg molluscs, corals have hard body parts made of calcium carbonate. When they die, their hard skeletons accumulate on the ocean floor and turn into sedimentary rock-like limestone

Causes of deforestation

Urbanisation-build houses, roads and factories

Agriculture-clear land to grow crops and rear livestock

Raw materials- wood is used as construction material, paper and fuel

Mining for rare earth metals

Effects of deforestation

1. Habitat loss→ especially bad for endangered/extinct wildlife→ loss of biodiversity

2. Global warming: Deforestation releases large amounts of carbon dioxide into atmosphere from decay and burning of wood + decreases number of trees that can remove and sequester atmospheric CO2

3. Soil erosion: no leaf canopy to protect soil from rain, no roots to bind the soil, no lea litter to slow down surface runoff

4. Soil compaction: soil becomes hard and dry as water evaporates quickly on exposed ground + trampling by animals squeeze out air pockets→difficult for plant roots and burrowing animals to penetrate soil→desertification (a

5. With forests, raindrops are intercepted by leaf canopy to slowly infiltrate the soil which is slowly released by transpiration. when forests are cleared, rainwater is lost quickly as surface runoff=less soil infiltrate ground= less transpiration=less clouds form over deforested area=less rainfall=desertification + bad for water cycle

Define pollution

Process where harmful contaminants are introduced into the environment, making it undesirable or unfit for life.

Describe all the steps of eutrophication

Step 1: Excessive nutrients from fertilisers are flushed from the land into rivers or lakes by rainwater

Step 2: nutrients cause flourishing aquatic plant growth of algae, duckweed, and other plants

Step 3: Algae blooms on surface of water body, preventing sunlight from reaching other submerged plants, causing plant to die and oxygen in the water slowly depleting because no more plants to carry out photosynthesis

Step 4: dead plants are broken down by aerobic bacteria decomposers, using up even more oxygen in the water

Step 5: oxygen reaches a point where no life is possible so fish and organisms die.

What do untreated sewage contain, are they biodegradable

Nutrients such as Nitrates and phosphates, which are biodegradable

And disease-causing organisms(pathogens)

Define and give examples of carbon sources

Carbon sources release more carbon than absorbed like fossil fuels when burnt, natural fires, and volcanic eruptions(small amount of carbon dioxide released)

What are insecticides and disadvantages

Insecticides are substances used to kill insects that destroy crops or spread diseases.

Disadvantages:

1. Insects may become resistant to the insecticides, making it ineffective after some time

2. Insecticides may kill beneficial insects

3. Insecticides may be carried by rainwater into nearby water bodies and accumulate in high concentrations in aquatic organisms (bio accumulation + bio magnification)

An example of insecticide is DDT, dichlorodiphenyltrichloroethane. Is it biodegradable? Is it soluble in water? What’s the effect because of this. What’s a harm DDT has on birds?

DDT is not biodegradable, so it cannot be broken down by bacteria and remains in soil and water for many years

DDT is insoluble in water, so it’s not excreted but stored in the fatty tissues of organisms that consume it. This leads to DDT being more concentrated in the consumer’s bodies over time(bioaccumulation) and biomagnification of DDT up trophic levels as top consumers accumulate the highest concentrations of DDT and suffer harmful effects

DDT causes eggshell thinning in birds, causing eggs to break easily during incubation, leading to population decline of birds of prey(predator)

Harmful impacts of plastics on environment and wildlife

1. Microplastics (<5mm) are non-biodegradable so they can bioaccumulate in their bodies, resulting in bioaccumulation in their bodies and biomagnification of microplastics up the food chain.

2. Burning of plastic releases CO2

3. Harmful chemicals from plastic waste buried in landfills may leach into rivers&Seas, poisoning aquatic wildlife

4. Plastic waste from disposables can trap, entangle or injured marine animals when washed into the sea.

Define conservation

Conservation is the protection and preservation of natural resources in the environment