Biology • Year 11 • Module 2 • Lesson 20
Autotrophs vs Heterotrophs, Full Synthesis
Consolidate the core vocabulary, the master comparison table, and the day/night gas exchange distinction that trips up students every year.
1. Term–definition match
The eight definitions below are shuffled. Write the matching term from the list into the right-hand column: autotroph, heterotroph, photosynthesis, cellular respiration, ATP, chloroplast, mitochondria, glucose. 8 marks
| # | Definition (shuffled) | Matching term |
|---|---|---|
| 1.1 | The universal energy currency of the cell; produced during cellular respiration and used to power active processes. | |
| 1.2 | An organism that obtains organic compounds by consuming other organisms or organic matter. | |
| 1.3 | A simple sugar produced by photosynthesis and broken down during cellular respiration to release energy. | |
| 1.4 | The organelle in plant cells where photosynthesis occurs, containing chlorophyll and thylakoid membranes. | |
| 1.5 | An organism that synthesises its own organic compounds from inorganic sources using light or chemical energy. | |
| 1.6 | The process by which cells break down glucose to release ATP energy; occurs in all living cells continuously. | |
| 1.7 | The organelle where aerobic respiration occurs, producing large amounts of ATP from glucose and oxygen. | |
| 1.8 | The process by which autotrophs convert light energy into chemical energy stored in glucose, releasing oxygen as a by-product. |
2. True or false, with correction
For each statement, circle T or F. If the statement is false, write the corrected version on the line provided. 10 marks (1 for T/F, 1 for correction where needed)
2.1 Plants stop performing cellular respiration at night because there is no light available. T / F
2.2 During bright daylight, a plant is a net producer of O&sub2; and a net consumer of CO&sub2;. T / F
2.3 Heterotrophs obtain organic carbon by fixing CO&sub2; from the atmosphere using light energy. T / F
2.4 Both autotrophs and heterotrophs perform cellular respiration. T / F
2.5 The light compensation point is the light intensity at which photosynthesis rate equals respiration rate, resulting in no net gas exchange. T / F
3. Complete the master comparison table
Fill in the missing cells. Each blank represents one key idea from the lesson. 12 marks
| Feature | Autotroph (plant) | Heterotroph (animal) |
|---|---|---|
| Energy source | Light energy captured by | Chemical energy released by breaking down |
| Carbon source | fixed from atmosphere by Calvin cycle | Organic carbon from food (glucose, amino acids, fatty acids) obtained by |
| Gas exchange structure | in leaves; lenticels in stems | in lungs (mammals) |
| Transport system type | Two vascular tissues: (water + minerals) and (sugars) | cardiovascular system; single transport medium: blood |
| Net O&sub2; at night | (consumed / released) | (consumed / released) |
| Nitrogen source | NO&sub3;− and NH&sub4;+ absorbed from soil via | Protein in food digested to amino acids; absorbed in |
4. Function recall
Answer each question in 1–2 sentences using precise terms from the lesson. 10 marks, 2 each
4.1 What is the function of stomata in a leaf with respect to gas exchange?
4.2 What is the function of the xylem in a plant’s transport system?
4.3 What is the function of alveoli in mammalian gas exchange?
4.4 What is the function of the liver with respect to urea in blood composition?
4.5 What is the function of the heart in a mammal’s cardiovascular system?
5. Connect the systems, concept map
Draw labelled arrows between the six terms below. Each arrow must carry a linking phrase (e.g. “is fixed by”, “is transported by”, “releases”). Aim for at least 6 labelled arrows. 6 marks
Supplied terms: photosynthesis · cellular respiration · glucose · ATP · CO&sub2; · O&sub2;
Q1, Term–definition matches
1.1 ATP • 1.2 heterotroph • 1.3 glucose • 1.4 chloroplast • 1.5 autotroph • 1.6 cellular respiration • 1.7 mitochondria • 1.8 photosynthesis.
Marking criteria: 1 mark per correct match. No mark if the organism is named without the term.
Q2, True / false with correction
2.1 False. Correction: cellular respiration occurs in all living plant cells continuously, 24 hours a day, regardless of light availability. Only photosynthesis stops at night.
2.2 True. During bright daylight, the rate of photosynthesis exceeds the rate of respiration, so net O&sub2; is released and net CO&sub2; is absorbed.
2.3 False. Correction: heterotrophs obtain organic carbon by consuming and digesting organic molecules made by autotrophs (or other organisms). It is autotrophs that fix CO&sub2; from the atmosphere using light energy.
2.4 True. All living cells, including those of plants, perform cellular respiration to produce ATP.
2.5 True. At the light compensation point, photosynthesis rate equals respiration rate and there is no net O&sub2; release or CO&sub2; absorption.
Marking criteria: 1 mark for correct T/F; 1 mark for a complete, accurate correction where F. No mark for the correction if it simply negates the statement without providing the correct biology.
Q3, Comparison table
Energy source (autotroph): chlorophyll / light reactions of photosynthesis. Energy source (heterotroph): organic molecules from food via cellular respiration.
Carbon source (autotroph): CO&sub2;. Carbon source (heterotroph): digestion (breaking down consumed organic molecules).
Gas exchange (autotroph): stomata. Gas exchange (heterotroph): alveoli.
Transport (autotroph): xylem (water + minerals) and phloem (sugars). Transport (heterotroph): closed (cardiovascular system).
Net O&sub2; at night (autotroph): consumed (only respiration occurs). Net O&sub2; at night (heterotroph): consumed (respiration is continuous in all organisms).
Nitrogen source (autotroph): root hairs. Nitrogen source (heterotroph): small intestine.
Marking criteria: 1 mark per correctly completed blank (12 blanks total). Accept equivalent phrasings that convey the correct biological meaning.
Q4.1, Function of stomata
Stomata are pores in the leaf epidermis that open and close to allow CO&sub2; to diffuse into leaf air spaces for photosynthesis and O&sub2; to diffuse out. They drive gas exchange by maintaining concentration gradients between the leaf interior and the atmosphere. Guard cells regulate stomatal opening in response to light and water availability.
Marking criteria: 1 mark for identifying CO&sub2; entry / O&sub2; exit by diffusion; 1 mark for linking to maintaining concentration gradients (or mentioning guard cell regulation).
Q4.2, Function of xylem
Xylem transports water and dissolved inorganic minerals from the roots upward through the stem and into the leaves. Water moves passively by the cohesion-tension mechanism driven by transpiration; the xylem sap loses mineral concentration as leaf cells absorb minerals for metabolic use.
Marking criteria: 1 mark for water + minerals transport; 1 mark for passive/cohesion-tension mechanism or direction (root to leaf).
Q4.3, Function of alveoli
Alveoli are tiny air sacs in the lungs that provide an enormous surface area for gas exchange. O&sub2; diffuses from alveolar air into pulmonary capillary blood down a partial pressure gradient; CO&sub2; diffuses in the reverse direction. Ventilation continuously replenishes alveolar O&sub2; and removes CO&sub2;, maintaining the gradients.
Marking criteria: 1 mark for O&sub2; in / CO&sub2; out by diffusion down partial pressure gradients; 1 mark for large surface area or mention of ventilation maintaining gradients.
Q4.4, Function of the liver (urea)
The liver produces urea by deaminating excess amino acids (a process called deamination). The toxic ammonia produced is converted to the less toxic urea in the urea cycle. Urea then enters the blood and is carried to the kidneys for excretion in urine. Blood urea concentration rises across the liver and falls across the kidneys.
Marking criteria: 1 mark for liver produces urea via deamination of amino acids; 1 mark for urea entering blood for excretion by kidneys.
Q4.5, Function of the heart
The heart is a muscular pump that contracts continuously to push oxygenated blood through arteries to all body tissues (systemic circuit) and deoxygenated blood through the lungs (pulmonary circuit). Cardiac muscle contraction requires ATP, making the heart itself a major consumer of the oxygen it distributes.
Marking criteria: 1 mark for pumping blood through the systemic/pulmonary circuit; 1 mark for mention of cardiac muscle / ATP requirement or that it maintains pressure.
Q5, Sample concept map
A correct map should include arrows such as:
- photosynthesisconverts CO&sub2; into → glucose
- photosynthesisreleases → O&sub2;
- photosynthesisconsumes → CO&sub2;
- glucoseis broken down by → cellular respiration
- cellular respirationproduces → ATP
- cellular respirationconsumes → O&sub2;
- cellular respirationreleases → CO&sub2;
Award 1 mark per correctly labelled, directionally accurate arrow. Any biologically valid linking phrase is accepted. Full marks for at least 6.