▶️ Answer/Explanation
a.
- Energy enters most ecosystems through sunlight. Plants (and other producers) absorb this light and convert it into chemical energy during photosynthesis. This is how they make their own food — sugars like glucose, which store energy.
- When animals eat the plants, the energy in the food passes up the food chain. As each animal eats another, some of that energy is used for movement, growth, and repair, while a lot is lost as heat (especially during cell respiration).
- Energy is also lost when organisms die and decompose or when waste like feces or urine is produced. Decomposers (like bacteria and fungi) break this down and use some of the remaining energy, but in the end, energy cannot be recycled — it keeps flowing through the system and is eventually lost as heat.
- Only about 10% of energy is passed from one level to the next. That’s why energy pyramids are wide at the bottom and narrow at the top.
b.
- Plants absorb phosphates and nitrates through their roots. These nutrients are essential for making important biological molecules.
- Phosphates help make:
- DNA and RNA (the molecules that carry genetic information),
- ATP (the energy currency of cells),
- and phospholipids (which are used in cell membranes).
- Nitrates are used to build:
- Amino acids, which are the building blocks of proteins,
- and also DNA, RNA, and ATP.
- Without these nutrients, plants wouldn’t be able to grow properly or make the molecules they need to survive.
c.
Markscheme:
a.
a. light energy is the initial energy source for (all) organisms
b. producers/autotrophs change light/radiant energy into chemical energy
OR
producers/autotrophs convert/trap light/radiant energy by photosynthesis
c. producing C6H12O6/sugars/carbohydrates
d. carbon/organic compounds used for energy/growth/repair/storage
e. compounds/energy pass as food along food chains/trophic levels WTTE
f. cellular respiration releases energy as ATP from food
g. energy is lost as heat (during cellular respiration)
h. loss of energy at each trophic level
OR
only approximately 10% of energy is passed to the next trophic level / 90% is lost at each trophic level
i. energy lost in bones/hair when they die/not fully eaten by the next trophic level
j. energy lost in feces/urine
k. decomposers/saprotrophs remove energy from wastes/bodies
l. energy is not recycled
b.
a. by photosynthesis / using energy from light
b. attached to carbon compounds
c. phosphates used to make phospholipids/nucleotides/nucleic acids/DNA/RNA/ATP
d. nitrates are used to make amino acids/proteins/nucleotides/nucleic acids/DNA/RNA/ATP
e. transported from roots to leaves (in xylem)
c.
a. drawn in steps rather than triangle
b. drawn to scale (should be at least 1/5 of the box below it)
OR
annotated with appropriate numeric values
c. producer
d. primary consumer
e. secondary consumer
▶️ Answer/Explanation
a.
Structure:
- Starch is a large carbohydrate made up of many glucose units joined together.
- It consists of two main types of molecules: amylose, which is a straight chain that coils into a helix, and amylopectin, which has a branched structure.
Function:
- Plants store glucose in the form of starch because it is compact and does not dissolve easily in water, meaning it won’t affect the plant’s water balance.
- It serves as an energy reserve, especially in parts like roots and seeds where the plant may need energy later.
b.
- Light energy from the Sun is absorbed by chlorophyll, mainly from red and blue wavelengths.
- This energy is used to split water molecules (a process called photolysis), releasing oxygen, hydrogen ions, and electrons.
- The energy is also used to make ATP and NADPH, which are energy-carrying molecules.
- Carbon dioxide from the air is fixed (converted into organic molecules) during the Calvin cycle.
- These reactions lead to the formation of glucose, which can be linked to form larger carbohydrates like starch for storage.
c.
- Carbon dioxide (CO₂) enters the atmosphere through processes like respiration by living organisms and the burning of fossil fuels and biomass.
- Methane (CH₄) is released by methanogenic microbes in places like wetlands, rice paddies, and the digestive systems of cows.
- Methane eventually breaks down in the atmosphere to form carbon dioxide and water.
- Plants remove carbon dioxide through photosynthesis, using it to make organic molecules.
- Some carbon is stored long-term in fossil fuels or as limestone, locking it out of the atmosphere.
- Both CO₂ and CH₄ are greenhouse gases—they trap heat in the atmosphere by absorbing infrared radiation.
- This trapping of heat leads to global warming and climate change, causing:
- Rising temperatures,
- Changing weather patterns,
- Ocean acidification, as oceans absorb more CO₂.
- Human activities like burning fossil fuels, deforestation, and farming (e.g., cattle and rice) are increasing levels of these gases and speeding up climate change.
Markscheme:
a. Structure:
a. Starch is a polysaccharide/composed of glucose molecules.
b. Contains amylose (linear/helical molecule).
c. Contains amylopectin (branched molecule).
Function:
d. Storage of glucose/energy in plants.
e. Storage form that does not draw water.
b.
a. Light absorbed by chlorophyll (prefers red/blue light).
b. Light energy → chemical energy.
c. Energy used to produce ATP.
d. Photolysis of water → O2/H+/NADPH.
e. CO2 fixation from air/water.
f. ATP/NADPH used to synthesize carbohydrates/starch.
c.
a. CO2 sources: respiration, combustion of biomass/fossil fuels.
b. CH4 sources: anaerobic respiration/methanogens.
c. CH4 oxidized → CO2 + H2O.
d. CO2 fixed by photosynthesis → carbohydrates.
e. CO2 sequestered as limestone/fossil fuels.
f. Greenhouse effect: CO2/CH4 trap long-wave radiation.
g. Consequences:
– Rising global temperatures.
– Climate pattern disruption.
– Ocean acidification (from CO2).
h. Human impacts: cattle/rice paddies/tundra thaw → ↑CH4.
▶️ Answer/Explanation
a.
b.
Photosynthesis is the process by which plants (autotrophs) make their own food using light energy, usually from the Sun.
Key steps:
- Reactants: Plants take in carbon dioxide (CO₂) from the air and water (H₂O) from the roots.
- Light absorption: Light is absorbed by chlorophyll in the chloroplasts, especially red and blue wavelengths.
- Photolysis: Light energy splits water into oxygen, protons, and electrons.
- Oxygen is released as a waste product.
- ATP and NADPH (energy carriers) are formed using the light energy.
- These molecules are used in the Calvin Cycle to fix carbon dioxide into glucose (C₆H₁₂O₆).
- Glucose can be stored as starch or used for energy in respiration.
c.
Peat forms when plant materials (like mosses, especially Sphagnum) accumulate in wet, waterlogged environments like bogs and swamps.
Key conditions for peat to form:
- Waterlogged soils create anaerobic (oxygen-poor) conditions.
- These conditions inhibit decomposers (like bacteria and fungi), so the dead plant material does not fully decompose.
- The environment is also acidic, which further slows down decomposition.
- Over thousands of years, partially decomposed plant material builds up and becomes peat.
Peat is an important carbon store, but when it’s drained or burned, it releases carbon dioxide, contributing to climate change.
Markscheme:
a. Palisade mesophyll cell structures not present in pancreatic cells:
- Cell wall (Must be shown as a double line)
- Large vacuole
- Chloroplast/plastid
- Starch grain
- Tonoplast
b. Process of photosynthesis:
- Autotrophs perform photosynthesis
- Carbon dioxide and water are the reactants/raw materials required
- Light splits water molecules/causes photolysis
- Photolysis releases oxygen as a waste product
- Light energy is converted into chemical energy
- Produces organic compounds/glucose/carbohydrates
- Occurs in chloroplasts
- Chlorophyll absorbs light (red and blue light/ends of the spectrum)
- Different pigments absorb different wavelengths of light
- Carbon dioxide concentration/temperature/light intensity are limiting factors
c. Process of peat formation:
- Formed from dead plant material/leaves/mosses/Sphagnum
- Forms in waterlogged sites/bogs/mires/swamps
- Occurs where bacteria/fungi/saprotrophs are not active/are inhibited
- Organic matter not fully decomposed
- Occurs in acidic conditions
- Occurs in anaerobic conditions (Reject: anaerobic respiration)
- Very slow process/takes a long time