Unit 4 - Energy, Environment, Microbiology & Immunity

What is photosynthesis?

Process by which living organisms capture the energy of the sun using chlorophyll + use it to convert CO₂ and H₂O into simple sugars

What does photosynthesis do?

Converts light into chemical energy (stored as glucose for respiration)

What is the chemical equation for photosynthesis?

6CO₂ + 6H₂O —> C₆H₁₂O₆ + 6O₂

What is ATP?

A nucleotide that acts as the universal energy supply in cells; made of adenine, ribose + 3 phosphate groups

What is ATP needed for?

Building new molecules, active transport, muscle contraction

What is the structure of ATP?

Phosphorylated nucleotide - nitrogenous base, sugar, 3 phosphate groups

How is ATP produced?

Adding Pi to ADP or when ETC releases energy for photophosphorylation

What occurs in the hydrolysis of ATP?

ATP —> ADP + Pi, catalysed by ATPase

What are the 2 stages of photosynthesis?

1. Light-dependent (LDS) = relies on light directly.

2. Light-independent (LIS) = relies on products of LDS

What happens in LDS and where does it occur?

Light converts into chemical energy as ATP and NADPH; occurs in thylakoid membrane

What occurs in non-cyclic photophosphorylation?

1. Light hits photosystem II.

2. 2e- excite, leave PSII and pass to 1st protein in ETC.

3. Release energy as passed down to enable chemiosmosis.

4. 2e- transfer to PSI at end of chain.

5. Light hits PSII again, exciting 2e- again.

6. 2e- + H+ + NADP → NADPH

7. NADPH + ATP pass to LIS.

How are the electrons used in non-cyclic phosphorylation replaced?

By photolysis of water

What is chemiosmosis?

1. H⁺ ions actively pump from low conc. in stroma to high conc. in thylakoid space.

2. H⁺ diffuse back to thylakoid membrane into stroma via ATP synthase enzymes embedded in membrane.

3. Movement of H⁺ ions causes ATP synthase enzymes to catalyse production of ATP.

What occurs in cyclic phosphorylation?

1. Light hits PSI.

2. 2e- are excited and leave photosystem, pass to 1st protein in ETC.

3. Pass down transport chain which releases energy, enables chemiosmosis.

4. 2e- rejoin PSI at end of chain.

5. ATP produced enters LIS.

What are the 3 stages of LIS?

1. CO₂ and RuBP combine.

2. Reduction of glycerate-3-phosphate.

3. Regeneration of RuBP.

What occurs when CO₂ and RuBP combine?

Produces unstable 6C compound, splits into 2 GP molecules (catalysed by rubisco).

CO₂ is fixed into plant cell.

What occurs in the reduction of glycerate-3-phosphate?

GP reduces to GALP via NADPH + ATP.

Some carbons from GALP produce organic molecules, rest remain to make RuBP again.

What occurs in the regeneration of RuBP?

5/6 GALP molecules are used to regenerate RuBP; requires ATP.

How many Calvin cycles are needed to create 1 glucose molecule?

6

What are the products of the LIS?

• Hexose sugars

• Glycerol

• Fatty acids

• Acetyl coenzyme A

• Nucleic acids

• Amino acids

What is a chloroplast?

Organelle in a plant cell where photosynthesis occurs.

What is the structure of a chloroplast?

Surrounded by double membrane, filled with cytoplasm-like fluid called stroma.

What is in the stroma?

Has enzymes, sugars, ribosomes + chloroplast DNA.

Have seperate system of membranes - thylakoids stack to form grana that are connected by lamellae.

What are thylakoids?

Multiple flattened, fluid-filled sacs which each have a membrane.

What is the function of the chloroplast envelope?

Keeps photosynthesis components close together.

Controls flow of molecules between stroma + cytoplasm.

What is the function of stroma?

Contains enzymes needed for photosynthesis.

What is the function of chloroplast DNA?

Contains genes that code for proteins used in photosynthesis.

What is the function of ribosomes in the chloroplast?

Enables translation of proteins coded by chloroplast DNA.

What is the function of the thylakoid space?

Conditions differ from stroma, has a small volume so proton gradient develops quickly for chemiosmosis.

What is the function of the grana?

Creates large surface area to maximise no. of photosystems + light absorption.

Provides more membrane area for proteins to enable ATP production.

What is the function of the photosystems?

Contains different combinations of photosynthetic pigments + each absorbs different wavelengths of light to maximise light absorption.

What light do chlorophylls reflect and what color does it appear?

Reflects blue-violet and red + appears green.

What light do cartenoids reflect and what color do they appear?

Reflects yellow and orange + appears blue-violet.

What is the absorption spectra?

Amount of light at different wavelengths absorbed by a particular pigment.

What is the action spectra?

Changing rate of photosynthesis at different wavelengths.

What is primary productivity?

Rate at which producers convert light energy into chemical energy.

What is gross primary productivity (GPP)?

Rate at which chemical energy is converted into carbohydrates during photosynthesis.

What is net primary productivity (NPP)?

Rate at which plant biomass is stored; GPP - plant respiratory losses (R).

How does the transfer of energy occur through a food chain?

Biomass is transferred from organism to organism when eaten so energy passes up the food chain.

How do energy losses occur for plants?

1. Light passes through leaves/reflects away.

2. Light hits non-photosynthetic areas.

3. Only certain wavelengths are absorbed.

4. Plants release energy during respiration.

Why is only 10% of an organism available to its consumer?

1. Full organism not eaten.

2. Not able to digest food.

3. Energy lost as heat when consumers respire.

4. Excretion of waste products.

What is net productivity?

Rate at which energy is converted into biomass.

What is the formula for energy efficiency?

(net productivity/energy received) * 100

What is a habitat?

The place where an organism lives.

What is a population?

All of the individuals of one species living in a habitat.

What is a community?

Multiple populations living and interacting in the same area.

What is an ecosystem?

A community and its interactions with the non-living parts of its habitats.

How does the availability of food affect a community?

More food = higher chance of surviving + reproducing; populations increase.

How do new predators affect a community?

More predators = less prey so unbalanced ecosystem; populations decrease.

How do new pathogens affect a community?

Populations will have no immunity/resistance; populations decrease.

How does competition affect a community?

2 species competing for same resources = one will outcompete; populations decrease.

How does light intensity affect a community?

More light = increased rate of photosynthesis + plant growth.

How does temperature affect a community?

Affects rate of photosynthesis.

How do moisture levels affect a community?

Plants + animals require water to survive.

How does soil pH and mineral content affect a community?

Different species are adapted to different soil pH + nutrient concentration levels.

How does wind intensity and direction affect a community?

Wind speed affects transpiration rate; affects photosynthesis as it ensures water + ions reach leaves.

How do CO₂ levels affect a community?

Required for photosynthesis.

How do O₂ levels affect a community?

Some aquatic animals require high O₂ levels.

What is a niche?

The role of a species within its habitat.

What happens if 2 species hold the same niche?

2 species will compete until one dies out.

What is abundance?

The number of individuals of a particular species living in a habitat.

What is distribution?

Where a species live.

How does a niche determine abundance?

Species occupying a similar niche will have lower abundance.

What is succession?

Process of ecosystem change over time.

What is primary succession?

Newly formed/exposed land is inhabited by an increasing number of species.

How can land be newly formed?

Magma from volcanoes cooling down to form rock surfaces.

How can land be newly exposed?

Landslides, glaciers that retreat, etc.

What are the stages of primary succession?

1. Seeds and spores carried by wind land on exposed rock and begin to grow.

2. Pioneer species die and decompose, forming soil.

3. Seeds of small plants and grasses grow in the soil.

4. Roots of small plants stabilize the soil.

5. Decomposition of small plants enriches and deepens the soil.

6. Larger plants, shrubs, and small trees grow.

7. Soil becomes deep, nutrient-rich, and retains water, supporting large trees.

8. Final species colonize and become dominant in a stable, complex ecosystem.

What are pioneer species?

First species to colonise land; can germinate easily, withstands harsh conditions.

What is a climax community?

Final community formed after succession.

How do newly arriving species change the environment?

They make it more suitable for species arriving later.

How do newly colonised species affect the environment?

They make the environment less suitable for previous species.

What is climate?

Weather conditions in a region over a long period of time.

What is climate change?

Significant changes in weather conditions in a region over a long period of time.

What are the 4 forms of evidence supporting climate change?

1. Atmospheric CO₂ levels

2. Average global temperatures

3. Changing plant communities

4. Dendrochronology

How do atmospheric CO₂ levels show climate change?

• Fluctuated due to volcanic eruptions + limestone weathering (evident from ancient ice core bubbles).

• Increased significantly since Industrial Revolution.

How do average global temperatures show climate change?

Records from mid 1800s (humans start burning fossil fuels) show increasing average temperature.

How do pollen grains preserve in peat bogs?

Dead plant matter gathers + becomes compact to form peat in layers; occurs in waterlogged + acidic conditions.

How do pollen grains in peat bogs show climate change?

Peat forms in layers so sample taken from bog is analysed microscopically.

E.g., plant needing warm conditions = gradual warming of climate due to adaptation.

How does dendrochronology show climate change?

Trees grow a new ring yearly (thicker ring = warmer conditions).

What is anthropogenic climate change?

Climate change due to human activities.

What is the greenhouse effect?

1. Radiation from sun hits earth + is radiated back from earth’s surface.

2. Greenhouse gas absorbs re-radiated radiation by trapping it in earth’s atmosphere so not lost in space.

What is the role of CO₂ in the atmosphere?

• Levels fluctuate due to volcanic eruptions + weathering limestone rocks.

• Industrial Revolution began from combusting fossil fuels which release CO₂.

• Also releases from carbon sinks.

What is the role of CH₄ in the atmosphere?

• Present as a gas in the atmosphere + main component of natural gas fossil fuel.

• Released from guts of ruminant mammals, decomposition of food waste in landfills, extraction of fossil fuels etc.

What is the carbon cycle?

1. Producers remove CO₂ from the atmosphere.

2. Carbon moves through consumers in food chains.

3. Organisms release CO₂ back into the atmosphere via respiration.

4. CO₂ dissolves in water + is used by marine plants for photosynthesis/to form CaCO₃ exoskeletons.

5. Partially decomposed matter forms peat or fossil fuels over millions of years.

6. Burning carbon sinks + biomass releases CO₂ into the atmosphere.

What are the three methods of environmental management?

1. Reduce combustion of fossil fuels.

2. Reduce combustion of biomass.

3. Reduce distribution of carbon pools.

What are climate change predictions used for?

• Building flood defences

• Funding scientific research

• Encouraging people to change activites

What are the limitations of climate change prediction models?

1. Does not show impact of future technologies

2. Unsure of effect of atmospheric gas concentrations on temperature

3. Complex global climate patterns

4. Factors apart from human activites

What are the impacts of increased atmospheric warming?

• Weather events become more extreme

• Changes to ocean currents

• More moisture changes rainfall patterns

What are the effects of warming climates?

• Species may not be able to outcompete others; decrease in biodiversity

• Plants cannot move; become extinct

What are the effects of changing water availability?

Species relying on seasonal rain may not survive e.g., desert plants.

What are the effects of changing seasonal cycles?

• Plants produce flowers earlier

• Animals produce offspring earlier

• Bird migration may lose synchronisation

What are the effects of retreating ice caps and glaciers?

May affect water supplies for people and surrounding wildlife.

What are the effects of rising sea levels?

Risk of flooding animals out of their habitats.

What is optimum temperature?

When an enzyme catalyses at the maximum rate.

What are the effects of lower temperatures on reactions?

Slow down reactions because of low kinetic energy - molecules move slowly, lower frequency of successful collisions, less likely for bonds to be formed or broken.

What are the effects of higher temperatures on reactions?

Accelerate reactions because of higher kinetic energy - molecules move quickly, more successful collisions so more likely for bonds to be formed or broken.

What happens in denaturation of enzymes?

If temperature increases past optimum, rate of reaction drops sharply - increased KE + vibration strains bonds of enzymes breaks shape of active site.

Tertiary structure breaks so shape is no longer complementary to substrate.

What is the temperature coefficient?

Increase in rate of reaction when temperature increases by 10 celsius.

Q10 = rate at higher temperature/rate at lower temperature.

What is evolution?

Changes in heritable characteristics of organisms over generations.