CDS Biology · Free notes
Plant Biology: CDS Biology
Plant Biology has 31 past-year questions in CDS General Knowledge, from 2018 (I) to 2026 (II): 12 EASY, 18 MODERATE and 1 HARD. Two papers carried seven each, 2018 (II) and 2024 (II), so the chapter comes in bursts. Nearly all are one-line recall: which tissue is dead, which hormone divides cells, which vegetable is a stem. The pairs that get swapped are the ones to learn exactly: xylem and phloem, transpiration and guttation, magnesium and manganese, and the apical, intercalary and lateral meristems.
The handout has every subtopic, worked example, formula and trap with answers shown. The formula sheet is the chapter’s formulas and traps alone, on one page.
Subtopic notes
Plant Organs
7 PYQsHow to tell a modified stem from a modified root, what a leaf does and how leaves are arranged, and how fruits form and seeds are carried away.
Tissues and Water Transport
13 PYQsWhere a plant grows (the meristems), the simple and complex permanent tissues, what xylem and phloem carry, and how water rises, escapes and is saved in dry and salty places.
Photosynthesis, Nutrients and Hormones
11 PYQsHow a leaf turns light, water and carbon dioxide into glucose, the pigments that catch the light, the mineral elements a plant needs, and the five plant hormones.
Formula & revision sheet
0 formulas · 11 reference tables · 22 gotchas across all subtopics — the exam-eve cheat-sheet
Formula & revision sheet
0 formulas · 11 reference tables · 22 gotchas across all subtopics — the exam-eve cheat-sheet
Plant Organs
Reference tables (3)
Modified roots and stems7 rows
| Plant part | What it really is |
|---|---|
| Potato | Underground stem (tuber); eyes are nodes with buds |
| Onion and garlic | Underground stem (bulb) with fleshy scale leavesQ CDS 2024 (I): potato, onion and garlic is the set of modified stems; carrot and turnip are roots. |
| Ginger and turmeric | Underground stem (rhizome) |
| Carrot, radish, turnip, sweet potato | Modified root |
| Pea tendril | Modified leaflet |
| Cactus spines | Modified leaves |
| Root hairs | The main absorbing surface of the plantQ CDS 2018 (II): the main absorbing organ of a plant is the root only. |
The leaf and its work7 rows
| Term | Meaning |
|---|---|
| Phyllotaxy | Arrangement of leaves on the stemQ CDS 2023 (II): phyllotaxy is the pattern of arrangement of leaves. |
| Alternate | One leaf at each node (mustard) |
| Opposite | Two leaves at each node, facing each other (guava) |
| Whorled | More than two leaves at a node (Alstonia) |
| Reticulate venation | Net of veins; dicots |
| Parallel venation | Veins side by side; monocots |
| Stomata | Pores for exchange of gases and loss of water vapour |
Fruits and seed dispersal7 rows
| Kind or agent | Examples |
|---|---|
| True fruit (from the ovary only) | Mango, tomato, pea podQ CDS 2018 (II): a true fruit is one where only the ovary grows into the fruit. |
| False fruit (thalamus included) | Apple, strawberry, cashew |
| Seedless (parthenocarpic) fruit | Banana |
| Dispersal by wind | Drumstick and maple (wings), cotton (hairs) |
| Dispersal by water | Coconut |
| Dispersal by animals | Xanthium (hooks), fleshy fruits that are eatenQ CDS 2018 (II): wind, water and animals disperse seeds; a fungus does not. |
| Dispersal by explosion | Balsam, castor |
Watch out for (6)
- Underground does not mean root→ Modified roots and stems
- Onion scales are leaves, the bulb is a stem→ Modified roots and stems
- Conduction is the stem's job→ The leaf and its work
- Phyllotaxy is leaves, not flowers→ The leaf and its work
- Thalamus and receptacle are the same part→ Fruits and seed dispersal
- Fungi do not disperse seeds→ Fruits and seed dispersal
Tissues and Water Transport
Reference tables (4)
Meristems: where a plant grows3 rows
| Meristem | Where | What it adds |
|---|---|---|
| Apical | Tips of root and shoot | Length |
| Intercalary | Base of the leaves or internodes | Length of leaf and internode; regrowth of grassQ Asked twice: CDS 2021 (II) and 2023 (I). The answer is the base of the leaves (or internodes), never the tip. |
| Lateral (vascular and cork cambium) | Sides of stem and root | Girth (secondary growth) |
Simple permanent tissues4 rows
| Tissue | Living or dead | Wall | Job |
|---|---|---|---|
| Parenchyma | Living | Thin, cellulose | Storage; photosynthesis as chlorenchyma |
| Collenchyma | Living | Thickened at the corners | Flexibility |
| Sclerenchyma | Dead | Thick, lignified | StrengthQ CDS 2020 (II): mature sclerenchyma cells have lignified walls and are dead. |
| Cork | Dead | Suberin | Protection; keeps water and gases out |
Xylem and phloem6 rows
| Element | Tissue | Living or dead |
|---|---|---|
| Tracheids and vessels | Xylem | Dead |
| Xylem parenchyma | Xylem | LivingQ CDS 2023 (I): of tracheid, vessel, xylem parenchyma and xylem fibre, only xylem parenchyma is living. |
| Xylem fibres | Xylem | Dead |
| Sieve tubes and companion cells | Phloem | Living |
| Phloem parenchyma | Phloem | Living |
| Phloem fibres | Phloem | Dead |
Two more questions ask what xylem carries: CDS 2018 (II) (a blocked xylem stops water AND solutes) and CDS 2024 (II) (water and dissolved minerals). CDS 2024 (II) also asks which is not part of a vascular bundle: the endodermis.
How water rises and escapes7 rows
| Term | Meaning |
|---|---|
| Transpiration | Loss of water as vapour through stomata |
| Guttation | Loss of water as liquid drops through hydathodesQ CDS 2018 (II): water escaping as droplets is guttation, not transpiration. |
| Cohesion | Water molecules holding on to each other |
| Adhesion | Water molecules holding on to the xylem walls |
| Xerophyte | Plant of dry places: small leaves, waxy cuticle, few sunken stomataQ CDS 2024 (II): a large number of stomata is NOT a feature of xerophytes. |
| Halophyte | Plant of saline soil, such as mangrovesQ CDS 2024 (II): halophytes grow on saline soil. |
| Hydrophyte | Plant of water, such as the water lily |
Watch out for (9)
- Intercalary is at the base, not the tip→ Meristems: where a plant grows
- Girth comes from the lateral meristem only→ Meristems: where a plant grows
- Lignin with sclerenchyma, suberin with cork→ Simple permanent tissues
- Two simple tissues are living→ Simple permanent tissues
- Xylem carries water AND minerals→ Xylem and phloem
- Phloem is complex, and it carries food→ Xylem and phloem
- Endodermis sits outside the bundle→ Xylem and phloem
- Respiration does not lift water→ How water rises and escapes
- Drops mean guttation→ How water rises and escapes
Photosynthesis, Nutrients and Hormones
Reference tables (4)
Photosynthesis4 rows
| Stage | Where | What happens |
|---|---|---|
| Light reactions | Thylakoids (grana) of the chloroplast | Light absorbed, water split, oxygen released, ATP and NADPH made |
| Calvin cycle (light-independent) | Stroma of the chloroplast | Carbon dioxide reduced to sugarQ CDS 2026 (II): the Calvin cycle is the light-independent part; the Hill reaction and photosystems need light. |
| Product | Leaf cells | Glucose, stored as starchQ CDS 2022 (I): plants prepare glucose by photosynthesis. |
| Starch test | A leaf from a sunny day | Boiled, decolourised in alcohol, turns blue-black with iodineQ CDS 2023 (I): the leaf ends up blue (blue-black) after the iodine test. |
Chlorophyll and carotenoids5 rows
| Pigment | Colour | Role |
|---|---|---|
| Chlorophyll a | Blue-green | Chief pigment; the reaction centre |
| Chlorophyll b | Yellow-green | Accessory pigment |
| Carotene | Orange | Accessory pigment; protects chlorophyllQ CDS 2026 (I): forming the reaction centre is NOT a function of carotenoids. |
| Xanthophyll | Yellow | Accessory pigment; protects chlorophyll |
| Where they sit | Chloroplast | In the thylakoid membranesQ CDS 2024 (II): the only structure in a leaf that hosts chlorophyll is the chloroplast. |
Macronutrients and micronutrients7 rows
| Element | Kind | One role |
|---|---|---|
| Nitrogen | Macronutrient | Part of proteins and chlorophyll |
| Phosphorus | Macronutrient | Part of nucleic acids and ATP |
| Potassium | Macronutrient | Opening and closing of stomata |
| Magnesium | Macronutrient | Centre of the chlorophyll moleculeQ CDS 2024 (II): magnesium is NOT a micronutrient; iron, manganese and chlorine are. |
| Iron | Micronutrient | Needed to make chlorophyll |
| Zinc | Micronutrient | Activates enzymes; needed for auxin |
| Boron | Micronutrient | Pollen germination, cell growth |
Plant hormones6 rows
| Hormone | Main effect |
|---|---|
| Auxin | Cell elongation; bending towards light |
| Gibberellins | Stem elongation; seed germination |
| Cytokinins | Cell division |
| Ethylene | Fruit ripening |
| Abscisic acid | Inhibits growth; dormancy; closes stomataQ CDS 2024 (II): the hormone that inhibits growth is abscisic acid. |
| Thyroxine | Not a plant hormone: made by the thyroid of animalsQ CDS 2025 (I): of gibberellins, abscisic acid, auxins and thyroxine, thyroxine is not a plant hormone. |
Watch out for (7)
- Carbon dioxide is reduced, not oxidised→ Photosynthesis
- The oxygen comes from water→ Photosynthesis
- Magnesium, not iron, in chlorophyll→ Chlorophyll and carotenoids
- Only chlorophyll a is the reaction centre→ Chlorophyll and carotenoids
- Magnesium and manganese are different→ Macronutrients and micronutrients
- Cytokinin divides, auxin lengthens→ Plant hormones
- Three promote, abscisic acid inhibits→ Plant hormones
PYQ weightage by concept
11 concepts · 31 PYQs — where the marks actually sit, so you know what to drill first
PYQ weightage by concept
11 concepts · 31 PYQs — where the marks actually sit, so you know what to drill first
Plant Organs7 PYQs · 23%
| Concept | PYQs | Share |
|---|---|---|
| Modified roots and stems | 3 | 10% |
| The leaf and its work | 2 | 6% |
| Fruits and seed dispersal | 2 | 6% |
Tissues and Water Transport13 PYQs · 42%
| Concept | PYQs | Share |
|---|---|---|
| Xylem and phloem | 5 | 16% |
| How water rises and escapes | 4 | 13% |
| Meristems: where a plant grows | 3 | 10% |
| Simple permanent tissues | 1 | 3% |
Photosynthesis, Nutrients and Hormones11 PYQs · 35%
| Concept | PYQs | Share |
|---|---|---|
| Photosynthesis | 4 | 13% |
| Chlorophyll and carotenoids | 3 | 10% |
| Plant hormones | 3 | 10% |
| Macronutrients and micronutrients | 1 | 3% |
Test yourself on Plant Biology
15 past CDS questions from this chapter, timed at 15 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.