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General Science Supplement for Forest Beat Officer · Chapter 2

Life Processes: Nutrition and Respiration

What to remember

  • Nutrition is how an organism obtains and uses food. Autotrophs (green plants) make their own food by photosynthesis. Heterotrophs depend on others: holozoic, saprotrophic or parasitic.
  • Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (in sunlight, with chlorophyll). It takes place in chloroplasts. Oxygen released comes from water.
  • Respiration releases energy from glucose and stores it as ATP. Aerobic respiration gives carbon dioxide, water and large energy. Anaerobic respiration gives less energy, with alcohol (yeast) or lactic acid (muscles).

Modes of nutrition

Autotrophic: green plants, algae and some bacteria make food from CO₂ and water using light (photoautotrophs).

Heterotrophic: cannot make their own food.

  • Holozoic: food is taken in whole and digested inside (humans, cow, Amoeba).
  • Saprotrophic: feed on dead and decaying matter (fungi such as mushroom and bread mould, many bacteria).
  • Parasitic: live on or in a host and harm it (Cuscuta or dodder, tapeworm, mosquito, Plasmodium).

Forest examples: Cuscuta is a total stem parasite with no chlorophyll. Sandalwood is a root hemiparasite; it has green leaves but takes water and minerals from the roots of host trees. Mycorrhiza is a partnership between fungi and tree roots. Insectivorous plants (pitcher plant, sundew, Venus flytrap) grow in nitrogen-poor soil and trap insects for nitrogen.

Photosynthesis

Requirements: sunlight, chlorophyll, carbon dioxide, water. The leaf takes CO₂ through stomata (tiny pores guarded by guard cells), and roots take water through xylem.

Steps

  • 1. Chlorophyll absorbs light energy.
  • 2. Light energy splits water into hydrogen and oxygen (light reaction, in the grana of the chloroplast).
  • 3. Carbon dioxide is reduced to carbohydrate (dark reaction or Calvin cycle, in the stroma).

Extra glucose is stored as starch. Iodine turns starch blue-black, which is used to test for photosynthesis in leaves.

Experiment points: a destarched plant kept in the dark shows no starch. Variegated leaves show starch only in the green parts. KOH absorbs CO₂, so a leaf in a flask with KOH does not photosynthesise.

Importance: gives food and oxygen, and takes in CO₂. Forests as large green areas act as carbon sinks.

Human nutrition

Nutrients: carbohydrates and fats (energy), proteins (growth and repair), vitamins and minerals (protection), water and roughage (fibre).

Digestive tract: mouth → oesophagus → stomach → small intestine → large intestine → anus.

OrganSecretionAction
MouthSalivary amylase (ptyalin)Starch → maltose
StomachPepsin, hydrochloric acid, mucusProtein breakdown; acid kills germs; mucus protects wall
LiverBile (stored in gall bladder)Emulsifies fats; makes food alkaline
PancreasTrypsin, lipase, amylaseProteins, fats, starch
Small intestineIntestinal juiceCompletes digestion (to glucose, amino acids, fatty acids and glycerol)

Absorption: takes place in the small intestine through finger-like villi, which increase surface area. The large intestine absorbs water. Undigested matter is removed as faeces (egestion).

Cud-chewing animals (cow, buffalo, deer) have a large stomach with a rumen. Bacteria there digest cellulose. Many forest herbivores such as deer and bison do this.

Nutrition in Amoeba: food is engulfed by pseudopodia in a food vacuole; digested; waste is thrown out.

Respiration

Cellular respiration happens in cells, mainly in mitochondria ("powerhouse of the cell"). Energy is stored as ATP (adenosine triphosphate).

Aerobic: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy.

  • Glycolysis in the cytoplasm: glucose (6C) → two pyruvate (3C).
  • Pyruvate enters mitochondria and is fully broken down.

Anaerobic

  • In yeast: glucose → ethanol + carbon dioxide + small energy (fermentation).
  • In muscles during heavy exercise: glucose → lactic acid. This causes cramps.
  • In some bacteria and in deep mud, anaerobic respiration is normal.
FeatureAerobicAnaerobic
OxygenNeededNot needed
End productsCO₂ + H₂OEthanol + CO₂ or lactic acid
EnergyLarge amount of ATPSmall amount
PlaceCytoplasm and mitochondriaCytoplasm only

Respiration is not breathing. Breathing is a physical process of taking in air. Respiration is a chemical process in cells.

Breathing in animals and plants

Humans: air passes through nose → pharynx → larynx → trachea → bronchi → bronchioles → alveoli (tiny air sacs with thin, moist walls, rich in blood capillaries). Gas exchange in alveoli: oxygen goes into blood, CO₂ leaves.

Mechanism: inhalation: diaphragm moves down, ribs move up and out, chest volume increases. Exhalation: diaphragm moves up, ribs move in and down.

Haemoglobin in red blood cells carries oxygen. It contains iron. Shortage of iron causes anaemia.

Other animals: earthworm breathes through moist skin, insects through tracheae (spiracles), fish through gills, frogs through skin and lungs.

Plants: gas exchange through stomata (leaves), lenticels (woody stems) and root surfaces. In the day, a plant photosynthesises more than it respires and gives out net oxygen. At night only respiration continues. Mangroves have breathing roots (pneumatophores) in waterlogged mud. The Godavari and Krishna deltas in Andhra Pradesh hold mangrove forests.

Extra points on nutrition and respiration

Balanced diet: it has carbohydrates, proteins, fats, vitamins, minerals, water and roughage in the right amounts. Roughage (fibre) is not digested but helps the movement of food.

NutrientSourceDeficiency
Vitamin ACarrot, papaya, liverNight blindness
Vitamin B₁Whole grainsBeriberi
Vitamin CAmla, citrusScurvy
Vitamin DSunlight, milk, fish oilRickets
Vitamin KGreen leafy vegetablesSlow blood clotting
IronLeafy vegetables, jaggeryAnaemia
CalciumMilk, ragiWeak bones
ProteinPulses, eggsKwashiorkor (and marasmus with low energy)

Digestion summary: carbohydrates become glucose, proteins become amino acids, and fats become fatty acids and glycerol. The first digestion of starch is in the mouth; protein digestion begins in the stomach; fat digestion mainly happens in the small intestine.

Gas exchange rate: a human at rest breathes about 15 to 18 times per minute. At 16 breaths per minute, a person breathes 16 × 60 = 960 times in an hour.

Photosynthesis and the environment: the rate of photosynthesis rises with light up to a limit, and is also influenced by carbon dioxide level and temperature. Plants in dense forest canopies are shade-adapted. Forest trees take in carbon dioxide and store carbon in wood, so forests act as carbon sinks.

Nutrition in other organisms: in Paramecium, food is taken in through a fixed cytostome. Hydra catches food with tentacles. In lichens, an alga and a fungus live together; the alga makes food and the fungus gives shelter and water (symbiosis). Root nodules of leguminous plants such as pongamia and subabul house Rhizobium bacteria that fix nitrogen.

Energy numbers: one molecule of glucose gives a net of about 2 ATP in glycolysis and many more in the mitochondria. Fermentation gives only the small glycolysis yield. Exact totals vary by textbook; remember that aerobic is far higher.

Test for nutrients: Benedict's solution gives an orange-red colour with glucose on heating. The biuret test gives a violet colour with protein. A grease spot on paper shows fat. Iodine gives a blue-black colour with starch.

Chlorophyll and light: chlorophyll absorbs mainly red and blue light and reflects green, so leaves look green. Leaves are broad and thin to catch light, and have many stomata on the lower side to reduce water loss. Xylem brings water and phloem takes food away.

Transpiration and photosynthesis: stomata open in the day to take in carbon dioxide; at the same time water vapour is lost. This is why a plant in a hot, dry spell may close its stomata and slow photosynthesis.

Exam traps

  • 1. Oxygen released in photosynthesis comes from water, not from carbon dioxide.
  • 2. Respiration vs breathing: chemical in cells vs physical movement of air.
  • 3. Aerobic gives the most ATP; fermentation gives little.
  • 4. Lactic acid is formed in muscles; ethanol in yeast.
  • 5. Pepsin works in acid in the stomach; trypsin in alkaline conditions in the small intestine.
  • 6. Bile contains no enzyme; it only emulsifies fat.
  • 7. Stomata vs lenticels: leaves vs woody stems.
  • 8. Cuscuta is a total parasite; sandalwood is a partial (hemi) parasite.

One-liners

  • 1. Chlorophyll is the green pigment for photosynthesis.
  • 2. Photosynthesis happens in chloroplasts.
  • 3. Starch is tested with iodine.
  • 4. Salivary amylase digests starch.
  • 5. Pepsin digests proteins in the stomach.
  • 6. Bile is made in the liver and stored in the gall bladder.
  • 7. Villi absorb digested food in the small intestine.
  • 8. Mitochondria are the sites of aerobic respiration.
  • 9. ATP is the energy currency of the cell.
  • 10. Alveoli are the sites of gas exchange in lungs.
  • 11. Haemoglobin carries oxygen.
  • 12. Yeast fermentation gives ethanol.

Practice questions

  1. Organisms that make their own food are called

    1. heterotrophs
    2. saprotrophs
    3. parasites
    4. autotrophs
    Answer

    D. autotrophs

    Autotrophs use light or chemical energy to make food.

  2. The site of photosynthesis in a plant cell is the

    1. ribosome
    2. mitochondrion
    3. nucleus
    4. chloroplast
    Answer

    D. chloroplast

    Chloroplasts contain chlorophyll.

  3. The oxygen released in photosynthesis comes from

    1. glucose
    2. water
    3. carbon dioxide
    4. chlorophyll
    Answer

    B. water

    Light splits water molecules.

  4. Tiny pores on the leaf surface for gas exchange are called

    1. root hairs
    2. lenticels
    3. xylem
    4. stomata
    Answer

    D. stomata

    Guard cells control the stomata.

  5. Iodine solution turns starch

    1. blue-black
    2. red
    3. colourless
    4. yellow
    Answer

    A. blue-black

    This is the starch test.

  6. Cuscuta (dodder) is an example of

    1. a saprotroph
    2. a total stem parasite
    3. a root hemiparasite
    4. an insectivorous plant
    Answer

    B. a total stem parasite

    It has no chlorophyll and lives on host stems.

  7. Sandalwood is best described as a

    1. total stem parasite
    2. saprotroph
    3. carnivorous plant
    4. root hemiparasite
    Answer

    D. root hemiparasite

    It has green leaves but takes water and minerals from host roots.

  8. Insectivorous plants such as pitcher plant trap insects mainly to get

    1. chlorophyll
    2. nitrogen
    3. sugar
    4. water
    Answer

    B. nitrogen

    They live in nitrogen-poor soils.

  9. Which organism shows saprotrophic nutrition?

    1. Cuscuta
    2. Amoeba
    3. Tapeworm
    4. Bread mould
    Answer

    D. Bread mould

    Fungi feed on dead organic matter.

  10. Salivary amylase acts on

    1. fat
    2. protein
    3. starch
    4. cellulose
    Answer

    C. starch

    It converts starch to maltose.

  11. Pepsin digests

    1. proteins
    2. fats
    3. starch
    4. vitamins
    Answer

    A. proteins

    It works in the acidic stomach.

  12. Bile juice is made in the

    1. liver
    2. pancreas
    3. gall bladder
    4. stomach
    Answer

    A. liver

    It is stored in the gall bladder but made in the liver.

  13. Bile helps in

    1. digestion of proteins
    2. absorption of water
    3. digestion of starch
    4. emulsification of fats
    Answer

    D. emulsification of fats

    Bile has no enzyme; it breaks fat into droplets.

  14. Digested food is absorbed mainly in the

    1. oesophagus
    2. large intestine
    3. small intestine
    4. stomach
    Answer

    C. small intestine

    Villi give a large surface area.

  15. The large intestine mainly absorbs

    1. proteins
    2. fats
    3. vitamins only
    4. water
    Answer

    D. water

    It dries the undigested food.

  16. Which enzyme is secreted by the pancreas?

    1. Pepsin
    2. Trypsin
    3. Bile
    4. Ptyalin
    Answer

    B. Trypsin

    Trypsin digests proteins in the small intestine.

  17. The powerhouse of the cell is the

    1. Golgi body
    2. lysosome
    3. mitochondrion
    4. vacuole
    Answer

    C. mitochondrion

    Aerobic respiration occurs there.

  18. The energy currency of the cell is

    1. RNA
    2. ATP
    3. glucose
    4. DNA
    Answer

    B. ATP

    Energy is stored in ATP.

  19. During heavy exercise, muscles produce

    1. ethanol
    2. carbon dioxide only
    3. oxygen
    4. lactic acid
    Answer

    D. lactic acid

    Anaerobic respiration in muscles gives lactic acid.

  20. Yeast respiring without oxygen produces

    1. lactic acid
    2. ethanol and carbon dioxide
    3. water and oxygen
    4. acetic acid only
    Answer

    B. ethanol and carbon dioxide

    This is fermentation.

  21. Glycolysis takes place in the

    1. cytoplasm
    2. mitochondrion
    3. nucleus
    4. chloroplast
    Answer

    A. cytoplasm

    Glucose is split into pyruvate there.

  22. Gas exchange in human lungs takes place in the

    1. bronchi
    2. trachea
    3. alveoli
    4. larynx
    Answer

    C. alveoli

    Alveoli are thin-walled sacs rich in capillaries.

  23. During inhalation the diaphragm

    1. moves down
    2. stays still
    3. moves up
    4. bursts
    Answer

    A. moves down

    The chest volume increases as the diaphragm flattens.

  24. The pigment that carries oxygen in blood is

    1. haemoglobin
    2. chlorophyll
    3. melanin
    4. insulin
    Answer

    A. haemoglobin

    It contains iron.

  25. Insects breathe through

    1. skin
    2. lungs
    3. gills
    4. tracheae
    Answer

    D. tracheae

    Air enters via spiracles into tracheae.

  26. Woody stems exchange gases through

    1. root caps
    2. lenticels
    3. guard cells
    4. stomata
    Answer

    B. lenticels

    Lenticels are small pores in bark.

  27. Mangroves have breathing roots called

    1. haustoria
    2. tendrils
    3. pneumatophores
    4. rhizoids
    Answer

    C. pneumatophores

    They take air in waterlogged mud.

  28. The number of ATP molecules is greatest in

    1. fermentation by yeast
    2. aerobic respiration
    3. lactic acid formation
    4. glycolysis only
    Answer

    B. aerobic respiration

    Complete breakdown of glucose gives the most energy.

  29. In photosynthesis, the dark reaction (Calvin cycle) takes place in the

    1. stroma
    2. cell wall
    3. mitochondria
    4. grana
    Answer

    A. stroma

    The light reaction takes place in the grana.

  30. Which chemical absorbs CO₂ in the experiment to show CO₂ is needed for photosynthesis?

    1. Sodium chloride
    2. Glucose
    3. Iodine
    4. Potassium hydroxide
    Answer

    D. Potassium hydroxide

    KOH removes CO₂ from the flask.

  31. The balanced equation for photosynthesis uses how many molecules of CO₂ for one molecule of glucose?

    1. 2
    2. 12
    3. 1
    4. 6
    Answer

    D. 6

    6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.

  32. If 3 molecules of glucose are completely oxidised in aerobic respiration, how many CO₂ molecules form?

    1. 6
    2. 18
    3. 12
    4. 3
    Answer

    B. 18

    Each glucose gives 6 CO₂; 3 × 6 = 18.

  33. If a plant forms 2 molecules of glucose, how many water molecules are needed (using the balanced equation)?

    1. 6
    2. 2
    3. 12
    4. 24
    Answer

    C. 12

    6 water per glucose; 2 × 6 = 12.

  34. Statements: 1. Respiration and breathing are the same process. 2. Respiration occurs in cells. Which is/are correct?

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

    B. 2 only

    Breathing is a physical process; respiration is chemical.

  35. Statements: 1. Bile contains digestive enzymes. 2. Pepsin works in an acidic medium. Which is/are correct?

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

    B. 2 only

    Bile has no enzyme.

  36. Statements: 1. Villi increase the surface area for absorption. 2. Villi are found in the stomach. Which is/are correct?

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

    A. 1 only

    Villi are in the small intestine.

  37. Statements: 1. Chlorophyll is needed for photosynthesis. 2. Photosynthesis takes place in mitochondria. Which is/are correct?

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

    A. 1 only

    It takes place in chloroplasts.

  38. Statements: 1. Amoeba takes in food with pseudopodia. 2. Amoeba shows saprotrophic nutrition. Which is/are correct?

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

    A. 1 only

    Amoeba is holozoic.

  39. Statements: 1. Aerobic respiration produces carbon dioxide and water. 2. Anaerobic respiration in yeast gives lactic acid. Which is/are correct?

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

    A. 1 only

    Yeast gives ethanol.

  40. Statements: 1. Cud-chewing animals digest cellulose with the help of bacteria. 2. Humans have a rumen. Which is/are correct?

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

    A. 1 only

    Humans do not have a rumen.

  41. Statements: 1. Leaves of a destarched plant kept in the dark will not show starch. 2. Variegated leaves show starch only in green parts. Which is/are correct?

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

    C. Both 1 and 2

    Both are true.

  42. Statements: 1. Plants release only oxygen at all times. 2. At night, plants carry out respiration only. Which is/are correct?

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

    B. 2 only

    Plants respire at all times; photosynthesis needs light.

  43. Statements: 1. Mycorrhiza is a partnership between fungi and plant roots. 2. Cuscuta contains chlorophyll. Which is/are correct?

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

    A. 1 only

    Cuscuta lacks chlorophyll.

  44. Statements: 1. Earthworms breathe through moist skin. 2. Fish breathe through lungs. Which is/are correct?

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

    A. 1 only

    Fish use gills.

  45. Statements: 1. Hydrochloric acid in the stomach kills germs. 2. Mucus protects the stomach wall. Which is/are correct?

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

    C. Both 1 and 2

    Both are true.

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