Unit notes and practice questions
Everything here is for unit 2 of the Grade 10 Biology textbook: what the chapter covers, the short notes, practice questions with their answers, and the lesson video where one exists.
The cards filed under this chapter on the Grade 10 Biology page. Open one at a time.
When you use it
Use when explaining directional growth responses of plant shoots and roots to unilateral light or gravity.
Watch out
The same auxin concentration that stimulates cell elongation in shoots inhibits cell elongation in roots.
Drafted from Grade 10 Biology, pages 17-49, then checked twice before it went up
| Feature | Dicot Seed | Monocot Seed |
|---|---|---|
| Cotyledons | Two cotyledons present | Only one cotyledon present |
| Cotyledon structure | Fleshy and stores food | Thin and lacks food materials |
| Endosperm | Absent | Large and well developed |
| Root development | Primary root bears lateral roots | Primary root replaced by fibrous roots |
When you use it
Use when comparing the anatomical structures and food storage parts of flowering plant seeds.
Watch out
Monocot seeds store nutrients in the endosperm, whereas dicot seeds store nutrients directly in the two fleshy cotyledons.
Drafted from Grade 10 Biology, pages 17-49, then checked twice before it went up
When you use it
Use when predicting the sequence of plant death resulting from removing a ring of bark.
Watch out
Girdling removes phloem while leaving xylem intact. The roots die first because downward food supply is halted, not because water transport stopped.
Drafted from Grade 10 Biology, pages 17-49, then checked twice before it went up
| Stage | Site in Chloroplast | Inputs | Outputs |
|---|---|---|---|
| Light reaction | Granum | Sunlight, | , ATP, |
| Dark reaction | Stroma | , ATP, | Glucose |
When you use it
Use when distinguishing the photochemical and enzymatic stages of photosynthesis and their specific locations.
Watch out
Oxygen is produced solely during the light reaction in the granum via photolysis of water, not from carbon dioxide in the dark reaction.
Drafted from Grade 10 Biology, pages 17-49, then checked twice before it went up
| Feature | Xylem | Phloem |
|---|---|---|
| Cell state | Elongated dead cells | Living cells |
| Transported materials | Water and dissolved minerals | Synthesized organic food |
| Direction of flow | Upward from root to leaves | Bidirectional between sources and sinks |
| Driving mechanism | Transpiration pull | Translocation |
When you use it
Use when comparing conducting vessels, transported materials, and transport mechanisms in vascular plants.
Watch out
Xylem transport is strictly upward and driven passively by transpiration pull, whereas phloem transport moves food in both directions through living cells.
Drafted from Grade 10 Biology, pages 17-49, then checked twice before it went up
| Factor | What happens as you raise it | What that tells you |
|---|---|---|
| Light intensity | The rate rises as the light rises, then levels off and stays flat. | The sloping part means light is the limit. The flat part means another factor has taken over. |
| Carbon dioxide concentration | The rate rises and then plateaus, the same shape the light curve makes. | Air holds only about 0.04% carbon dioxide, so in bright sunlight this is very often the limit. |
| Temperature | The rate climbs to an optimum and then falls steeply above it. For common crop plants the optimum is a band of roughly 25 °C to 35 °C. | The fall is the enzymes being denatured by heat. Near 0 °C the rate is close to zero. |
| Water | A plant short of water slows down, although only a little of the water it takes up is used in the reaction. | The plant closes its stomata to save water, and closed stomata cut off the carbon dioxide supply. |
| Chlorophyll | Less healthy green tissue means a lower rate. | Light is absorbed by chlorophyll, so leaf disease or a magnesium shortage lowers the rate the way shade does. |
When you use it
Use it when a question asks why the rate of photosynthesis stopped rising, or what to change so a plant produces more. The rate is set by whichever condition is in shortest supply, so raising any of the others changes nothing until that one is raised.
Watch out
Two mistakes cost marks here. The temperature curve is not shaped like the light curve: it peaks and then drops steeply, because heat denatures the enzymes. And when the light curve goes flat, the answer is not that the plant now has enough light. Name what took over: carbon dioxide concentration or temperature is holding the rate down, and more light cannot move it.
| Step | What you do | Why it matters |
|---|---|---|
| 1. Destarch | Keep the potted plant in complete darkness for 24 to 48 hours, then test one leaf with iodine to confirm no starch is left. | Starch stored before the experiment turns the whole leaf blue-black and the result proves nothing. |
| 2. Cover | Clip black paper or aluminium foil over part of one leaf, on both surfaces, and leave the rest of that leaf uncovered. | Cover the upper face only and light still reaches the leaf from below, so the covered part makes starch anyway. |
| 3. Give light | Stand the plant in bright sunlight for about 4 to 6 hours. | This is the only time photosynthesis is allowed to run, so any starch you find was made now. |
| 4. Boil in water | Take the leaf off and boil it in water for about a minute. | It kills the cells, stops the reactions and makes the membranes permeable. |
| 5. Boil in ethanol | Stand the ethanol in a hot water bath and boil the leaf in it until the leaf goes pale. | The ethanol dissolves the chlorophyll out. It is flammable, so it is never heated over a flame. |
| 6. Add iodine | Dip the pale leaf in hot water to soften it, spread it on a white tile and cover it with iodine solution. | Hot water opens the brittle leaf flat, and iodine is the test for starch. |
| 7. Read the result | The uncovered part turns blue-black. The covered part stays the yellow-brown colour of the iodine itself. | Starch formed only where light reached the leaf, so light is necessary for photosynthesis. |
When you use it
Use it for the practical that shows light is needed for photosynthesis, and for questions asking why each step is done. The covered part of the same leaf is the control: it shares the plant, the water, the carbon dioxide and the temperature, so light is the only thing that differs.
Watch out
Students skip the destarching and go straight to the sunlight. Both parts then turn blue-black, because the starch was in the leaf before the experiment started, and the student writes down that light is not needed. The other common slip is dropping a green leaf straight into iodine: with the chlorophyll still in it, no colour change can be seen at all.
10 multiple-choice questions written against this chapter, each with its answer and the reason. Try one before you open the answer.
Question 1
Which reproductive structure is found in gymnosperms like Podocarpus falcatus (Zigba) and Juniperus procera (Tid) instead of flowers?
Answer: A Cones
Why
Gymnosperms do not have flowers or fruits. Instead, their reproductive organs are cones, which produce naked seeds.
Question 2
What is the rigid cell wall of a plant cell mainly made of?
Answer: B Cellulose
Why
Plant cells are surrounded by a rigid cell wall made primarily of cellulose.
Question 3
Which female part of a flower consists of the ovary, style, and stigma?
Answer: C Pistil
Why
The pistil (also called carpel or gynoecium) is the female reproductive part consisting of the stigma, style, and ovary.
Question 4
What happens to the cotyledon during hypogeal seed germination?
Answer: B It remains under the soil
Why
In hypogeal germination, the cotyledon stays beneath the ground. In epigeal germination, the cotyledon is pushed above the soil surface.
Question 5
Which tissue layer inside a leaf contains the greatest number of chloroplasts per cell to carry out most of the photosynthesis?
Answer: C Palisade layer
Why
The palisade layer is positioned right below the upper epidermis and contains closely packed columnar cells with the largest number of chloroplasts per cell.
Question 6
Why do healthy green plant leaves appear green to our eyes?
Answer: A Green light wavelengths are reflected instead of absorbed
Why
Chlorophyll absorbs light in the blue (400 to 500 nm) and red (600 to 700 nm) ranges, but green light (500 to 600 nm) is not absorbed and is reflected.
Question 7
What is the term for the light-driven splitting of water molecules into hydrogen ions and oxygen in the granum?
Answer: C Photolysis
Why
During the light reaction in the granum, light energy splits water molecules (H2O) into H+ and O2. This process is called photolysis.
Question 8
How does phloem tissue differ from xylem tissue in vascular plants?
Answer: A Phloem contains living cells that translocate food in both directions
Why
Phloem consists of living cells that actively transport organic food (sucrose and amino acids) up and down the plant, while xylem is made of dead cells transporting water and minerals upward.
Question 9
In a tree girdling experiment, a ring of bark containing the phloem is removed from the stem. Why does the plant root die first?
Answer: B Translocation of food from the leaves to the root is stopped
Why
Removing the phloem disrupts food transport from the leaves to the sink tissues below. The roots die first because they are starved of organic food.
Question 10
In Charles Darwin's phototropism experiment, which condition prevented a young seedling shoot from bending toward light?
Answer: B Covering the tip of the shoot with an opaque foil
Why
Darwin showed that when the tip of the coleoptile is removed or covered with opaque foil, the shoot fails to detect light and does not bend.
The app holds 12 questions on this unit, marked as you go. These are the first 10.
Unit 2 runs from page 17 to page 49 of the Ministry of Education edition.
Ministry of Education edition, English, 177 pages
Temari turns this chapter into timed practice and marks it as you go, with an AI tutor to explain anything that did not land.
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