Botany: Plant Life Processes

What to remember

• Plants make their own food by photosynthesis in green parts, using sunlight, carbon dioxide and water. Oxygen is released.
• Xylem carries water up; phloem carries food up and down. Respiration releases energy from food in all living cells, day and night.
• Plant hormones and tropisms control growth. Auxin helps stems grow toward light; gibberellin helps stem growth; cytokinin helps cell division; abscisic acid slows growth; ethylene ripens fruit.

Nutrition in plants

Plants are autotrophs (they make their own food). Animals and fungi are heterotrophs.

Photosynthesis happens mainly in leaves, inside chloroplasts, which hold the green pigment chlorophyll.

Light energy + 6CO2 + 6H2O gives glucose (C6H12O6) + 6O2.

Steps:

• 1. Chlorophyll absorbs sunlight.
• 2. Light energy splits water into hydrogen and oxygen.
• 3. Carbon dioxide is reduced to carbohydrate using the hydrogen.
• 4. Oxygen leaves through the stomata.

Extra glucose is stored as starch. A leaf kept in the dark and then tested with iodine does not turn blue-black, because there is no starch.

Conditions needed: sunlight, chlorophyll, carbon dioxide and water. The rate rises with light and CO2 up to a limit.

Stomata are tiny pores on leaves. Each pore is guarded by two guard cells, which open or close it. Stomata let in CO2, let out oxygen and water vapour. Most plants open them in the day and close them at night.

Other modes of nutrition

Cuscuta has no chlorophyll and is a total parasite. Rhizobium bacteria live in root nodules of legumes such as groundnut and pigeon pea. They fix atmospheric nitrogen into usable form.

Minerals: Nitrogen helps leaf growth; phosphorus helps roots; potassium helps flowering and disease resistance; magnesium is part of chlorophyll; iron is needed for chlorophyll formation. A yellow leaf from lack of chlorophyll is called chlorosis.

Transport in plants

Plants have two types of conducting tissue (vascular tissue).

Absorption: Root hairs absorb water from soil by osmosis. Osmosis is the movement of water from a dilute solution to a concentrated solution through a semi-permeable membrane.

Transpiration is the loss of water vapour from aerial parts, mostly through stomata. It pulls water up the stem, cools the plant and helps minerals move. Transpiration is faster in hot, dry, windy conditions and slower in humid air.

Guttation is the loss of liquid water drops from leaf tips at night, through special pores called hydathodes, due to root pressure.

Respiration in plants

All living cells respire to release energy (ATP) from food. It happens in the mitochondria.

• Aerobic respiration (uses oxygen): glucose + oxygen gives carbon dioxide + water + energy. It gives much more energy.
• Anaerobic respiration (no oxygen): in yeast, glucose gives ethanol + carbon dioxide + a little energy. This is fermentation. In our muscles during hard exercise, it gives lactic acid.

Plants have no lungs. Gas exchange happens through stomata in leaves, lenticels in woody stems and the surface of roots. Photosynthesis and respiration are opposite in nature: photosynthesis stores energy and uses CO2, while respiration releases energy and gives out CO2.

Reproduction in plants

Asexual reproduction needs only one parent and gives offspring identical to the parent.

• Vegetative propagation: new plants from roots, stems or leaves. Potato (tuber), ginger (rhizome), onion (bulb), rose and sugarcane (stem cutting), and Bryophyllum (leaf buds).
• Budding: yeast.
• Spore formation: fungi, ferns.
• Fragmentation: Spirogyra.
• Tissue culture: growing a plant from a small piece of tissue in a nutrient medium in a laboratory.
• Grafting and layering are used for mango and jasmine.

Sexual reproduction is through flowers.

• Flower parts: sepals (calyx), petals (corolla), stamens (male) and carpels or pistil (female).
• Stamen: anther (makes pollen) and filament.
• Pistil: stigma, style and ovary. The ovary holds ovules.
• Pollination: transfer of pollen from anther to stigma. It may be self-pollination or cross-pollination. Agents are wind, insects, water and birds.
• Fertilisation: the male gamete joins the female gamete in the ovule to form a zygote. After it, the ovule becomes the seed and the ovary becomes the fruit.
• Double fertilisation is a feature of flowering plants (angiosperms).

Seed dispersal protects species from crowding. Wind carries light seeds such as dandelion and maple. Water carries coconut. Animals carry burs. Explosion in dry fruits is seen in castor and balsam.

Germination needs water, air (oxygen) and suitable warmth. Light is not needed for most seeds.

Tropisms and plant hormones

A tropism is a directional growth movement in response to a stimulus.

Shoots show positive phototropism and negative geotropism. Roots show negative phototropism and positive geotropism. Nastic movement is not directional; for example, the leaves of the touch-me-not plant (*Mimosa pudica*) fold when touched.

Plant hormones

Auxin was first found in coleoptile tip experiments on oats. Auxin collects on the shaded side of a shoot and makes those cells grow longer, so the shoot bends toward light.

Plant tissues and structure

Plant tissues are of two main groups.

A root anchors the plant, absorbs water and minerals, and sometimes stores food (carrot, radish, beetroot). A stem holds leaves and flowers and carries materials. A leaf is the food factory. Leaf parts are the blade (lamina), the midrib and veins, and the petiole. Parallel venation is seen in monocots such as grass and wheat; reticulate venation is seen in dicots such as mango and hibiscus.

Monocot and dicot seeds: A monocot seed (maize, rice) has one cotyledon. A dicot seed (gram, bean) has two cotyledons. The cotyledon stores food for the baby plant (embryo).

Pollination types: In self-pollination, pollen goes to the stigma of the same flower or the same plant. In cross-pollination, pollen goes to another plant of the same kind and gives more variety. Bright petals, scent and nectar attract insects. Wind-pollinated flowers are small and make a lot of light pollen.

Exam traps

• Xylem carries water; phloem carries food. Xylem cells are dead; phloem cells are living.
• Stomata are in leaves; lenticels are in woody stems.
• Oxygen released in photosynthesis comes from water, not from carbon dioxide.
• Photosynthesis needs light; respiration goes on all the time.
• Mushrooms are saprophytes; Cuscuta is a parasite; Pitcher plant is insectivorous.
• Transpiration is loss of water vapour; guttation is loss of liquid water.
• Ethylene ripens fruits; cytokinin divides cells; abscisic acid inhibits growth.
• Bryophyllum reproduces through leaf buds; potato through tubers; ginger through rhizomes.

One-liners

• 1. Chlorophyll is the green pigment that traps light.
• 2. Photosynthesis takes place in chloroplasts.
• 3. Starch is the stored food of plants.
• 4. Guard cells control the opening of stomata.
• 5. Xylem carries water and minerals upward.
• 6. Phloem carries prepared food.
• 7. Respiration takes place in mitochondria.
• 8. Yeast shows fermentation without oxygen.
• 9. Stamen is the male part of a flower; pistil is the female part.
• 10. Pollination is the transfer of pollen to the stigma.
• 11. Tissue culture grows plants from small pieces of tissue.
• 12. Ethylene is the fruit-ripening hormone.

Practice questions

1. Plants that make their own food are called

   1. Parasites
   2. Heterotrophs
   3. Saprophytes
   4. Autotrophs
   Answer

   D. Autotrophs

   Autotrophs prepare food by photosynthesis.

2. Photosynthesis mainly takes place in the

   1. Mitochondria
   2. Chloroplasts
   3. Nucleus
   4. Ribosomes
   Answer

   B. Chloroplasts

   Chloroplasts hold chlorophyll.

3. The green pigment that traps sunlight is

   1. Carotene
   2. Chlorophyll
   3. Melanin
   4. Haemoglobin
   Answer

   B. Chlorophyll

   Chlorophyll absorbs light for photosynthesis.

4. The oxygen released during photosynthesis comes from

   1. Carbon dioxide
   2. Starch
   3. Glucose
   4. Water
   Answer

   D. Water

   Light splits water molecules to release oxygen.

5. Extra glucose made by a plant is stored as

   1. Cellulose sheet
   2. Protein
   3. Starch
   4. Glycogen
   Answer

   C. Starch

   Plants store carbohydrate as starch.

6. The tiny pores on leaves for gas exchange are the

   1. Lenticels
   2. Hydathodes
   3. Root hairs
   4. Stomata
   Answer

   D. Stomata

   Stomata let in CO2 and release oxygen and water vapour.

7. Stomata are opened and closed by

   1. Root hairs
   2. Guard cells
   3. Sieve tubes
   4. Companion cells
   Answer

   B. Guard cells

   Two guard cells surround each stoma.

8. Cuscuta (dodder), which has no chlorophyll, is a

   1. Saprophyte
   2. Insectivorous plant
   3. Symbiont
   4. Parasite
   Answer

   D. Parasite

   It takes food from its host plant.

9. Which plant traps insects to get nitrogen?

   1. Cuscuta
   2. Rose
   3. Pitcher plant
   4. Mushroom
   Answer

   C. Pitcher plant

   Pitcher plant is insectivorous.

10. Rhizobium bacteria in root nodules of legumes

    1. Absorb water by osmosis
    2. Fix atmospheric nitrogen
    3. Make chlorophyll
    4. Cause chlorosis
    Answer

    B. Fix atmospheric nitrogen

    They convert atmospheric nitrogen into a usable form.

11. The mineral that is a part of the chlorophyll molecule is

    1. Calcium chloride
    2. Magnesium
    3. Sodium
    4. Potassium
    Answer

    B. Magnesium

    Magnesium sits at the centre of chlorophyll.

12. Water and minerals move upward in the plant through the

    1. Epidermis
    2. Phloem
    3. Cambium
    4. Xylem
    Answer

    D. Xylem

    Xylem is the water-conducting tissue.

13. Prepared food is moved through the plant by the

    1. Cuticle
    2. Guard cells
    3. Phloem
    4. Xylem
    Answer

    C. Phloem

    Translocation happens in phloem.

14. Which statement about xylem is correct?

    1. It carries sugar downward only
    2. It uses ATP for translocation
    3. Its conducting cells are dead
    4. It has sieve tubes
    Answer

    C. Its conducting cells are dead

    Xylem vessels and tracheids are dead.

15. Loss of water vapour from the aerial parts of a plant is called

    1. Translocation
    2. Transpiration
    3. Guttation
    4. Osmosis
    Answer

    B. Transpiration

    Most of it occurs through stomata.

16. Drops of liquid water coming out of leaf tips at night is

    1. Fermentation
    2. Respiration
    3. Transpiration
    4. Guttation
    Answer

    D. Guttation

    Guttation occurs through hydathodes due to root pressure.

17. Transpiration will be fastest when the air is

    1. Hot, dry and windy
    2. Cool and humid
    3. Foggy
    4. Cold and still
    Answer

    A. Hot, dry and windy

    Dry, warm moving air takes up water vapour quickly.

18. Respiration in cells takes place mainly in the

    1. Cell wall
    2. Mitochondria
    3. Chloroplasts
    4. Vacuole
    Answer

    B. Mitochondria

    Mitochondria release energy from food.

19. When yeast respires without oxygen, it produces ethanol and

    1. Starch
    2. Lactic acid
    3. Carbon dioxide
    4. Oxygen
    Answer

    C. Carbon dioxide

    This is alcoholic fermentation.

20. In woody stems, gas exchange takes place through

    1. Stomata only
    2. Lenticels
    3. Hydathodes
    4. Root cap
    Answer

    B. Lenticels

    Lenticels are small openings in bark.

21. Potato reproduces vegetatively by

    1. Bulbs
    2. Rhizomes
    3. Leaf buds
    4. Tubers
    Answer

    D. Tubers

    Potato eyes on a tuber grow into new plants.

22. Bryophyllum reproduces by

    1. Leaf buds
    2. Runners
    3. Spores
    4. Stem tuber
    Answer

    A. Leaf buds

    Buds on leaf margins grow into new plants.

23. Growing a whole plant from a small piece of tissue in a nutrient medium is

    1. Pollination
    2. Layering
    3. Tissue culture
    4. Grafting
    Answer

    C. Tissue culture

    It is done in a laboratory under sterile conditions.

24. The male reproductive part of a flower is the

    1. Carpel
    2. Pistil
    3. Sepal
    4. Stamen
    Answer

    D. Stamen

    The anther of a stamen produces pollen.

25. Transfer of pollen from anther to stigma is called

    1. Germination
    2. Fertilisation
    3. Dispersal
    4. Pollination
    Answer

    D. Pollination

    Fertilisation comes after pollination.

26. After fertilisation in a flower, the ovary develops into the

    1. Pollen
    2. Fruit
    3. Seed
    4. Stigma
    Answer

    B. Fruit

    The ovule becomes the seed and the ovary the fruit.

27. Seed germination needs

    1. Water, air and suitable warmth
    2. Only sunlight
    3. Only fertiliser
    4. Only chlorophyll
    Answer

    A. Water, air and suitable warmth

    Most seeds need no light to germinate.

28. The bending of a shoot toward light is

    1. Negative geotropism only
    2. Hydrotropism
    3. Thigmotropism
    4. Positive phototropism
    Answer

    D. Positive phototropism

    Shoots grow toward the light source.

29. Tendrils coiling around a support show

    1. Hydrotropism
    2. Chemotropism
    3. Thigmotropism
    4. Phototropism
    Answer

    C. Thigmotropism

    Thigmotropism is a response to touch.

30. The growth of the pollen tube toward the ovule is an example of

    1. Chemotropism
    2. Thigmotropism
    3. Geotropism
    4. Phototropism
    Answer

    A. Chemotropism

    Chemicals from the ovule guide the tube.

31. The hormone that ripens fruits is

    1. Cytokinin
    2. Gibberellin
    3. Ethylene
    4. Auxin
    Answer

    C. Ethylene

    Ethylene is a gas that ripens fruit.

32. The hormone that promotes cell division is

    1. Cytokinin
    2. Abscisic acid
    3. Ethylene
    4. Auxin only for fruit ripening
    Answer

    A. Cytokinin

    Cytokinin also delays leaf ageing.

33. A growth inhibitor that also helps close stomata in dry conditions is

    1. Cytokinin
    2. Abscisic acid
    3. Gibberellin
    4. Auxin
    Answer

    B. Abscisic acid

    ABA is the stress hormone of plants.

34. Consider the statements about photosynthesis and respiration. 1. Photosynthesis happens only in cells with chlorophyll. 2. Respiration happens in plants only at night.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Respiration goes on day and night.

35. Consider the statements about plant transport. 1. Xylem and phloem both carry water only. 2. Phloem carries prepared food.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    B. 2 only

    Xylem carries water; phloem carries food.

36. Consider the statements about stomata. 1. They help in the exchange of gases. 2. They are present on the roots of all plants as root hairs.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Root hairs are different from stomata.

37. Consider the statements about hormones. 1. Auxin helps a shoot bend toward light. 2. Gibberellin helps stem elongation.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both are correct.

38. Consider the statements about tropisms. 1. Roots show positive geotropism. 2. Shoots show positive geotropism.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Shoots show negative geotropism.

39. Consider the statements about nutrition. 1. Mushroom is a saprophyte. 2. Lichen is a total parasite.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Lichen is symbiosis between algae and fungus.

40. Consider the statements about flowering plants. 1. Pollination is followed by fertilisation. 2. Double fertilisation occurs in angiosperms.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both are correct.

41. Consider the statements about the touch-me-not plant (Mimosa pudica). 1. Its leaves fold when touched. 2. The movement is directional and called a tropism.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    It is a nastic movement, not directional.

42. Consider the statements about anaerobic respiration. 1. It happens without oxygen. 2. In human muscles, it can produce lactic acid.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both are correct.

43. Match the plant (left) with its method of reproduction (right). P. Ginger Q. Yeast R. Spirogyra S. Ferns

    1. P-budding, Q-rhizome, R-fragmentation, S-spores
    2. P-rhizome, Q-fragmentation, R-budding, S-spores
    3. P-rhizome, Q-budding, R-spores, S-fragmentation
    4. P-rhizome, Q-budding, R-fragmentation, S-spores
    Answer

    D. P-rhizome, Q-budding, R-fragmentation, S-spores

    Ginger has a rhizome, yeast buds, Spirogyra fragments, ferns form spores.

44. Match the hormone (left) with its role (right). P. Auxin Q. Cytokinin R. Ethylene S. Abscisic acid

    1. P-fruit ripening, Q-cell division, R-cell elongation, S-growth inhibition
    2. P-cell elongation, Q-cell division, R-fruit ripening, S-growth inhibition
    3. P-cell division, Q-cell elongation, R-fruit ripening, S-growth inhibition
    4. P-cell elongation, Q-cell division, R-growth inhibition, S-fruit ripening
    Answer

    B. P-cell elongation, Q-cell division, R-fruit ripening, S-growth inhibition

    Each hormone matches its main role in option A.

45. Match the mode of nutrition (left) with the example (right). P. Parasitic Q. Saprophytic R. Insectivorous S. Symbiotic

    1. P-bread mould, Q-Cuscuta, R-sundew, S-lichen
    2. P-sundew, Q-bread mould, R-Cuscuta, S-lichen
    3. P-Cuscuta, Q-bread mould, R-lichen, S-sundew
    4. P-Cuscuta, Q-bread mould, R-sundew, S-lichen
    Answer

    D. P-Cuscuta, Q-bread mould, R-sundew, S-lichen

    The pairs in option A are standard examples.