Green plants are the only living things that can turn sunlight into food. That food feeds every animal, including us. The oxygen they give off keeps the air fit to breathe. Punjab, the food bowl of India, also lives by the second half of this chapter: which crop is sown when, how soil is fed and watered, and how pests are controlled.
On this page you will learn:
- Photosynthesis, chlorophyll and why trees give off CO2 at night
- Plant nutrition: root nodules, parasites and plant poisons
- Kharif, rabi and zaid crops of Punjab
- Ploughing, cropping patterns, manure and fertilisers
- Pests, Bt cotton and ripening of fruit
- The Green, White and other farm revolutions
Mg
Metal at the centre of chlorophyll
Magnesium
3
Crop seasons
Kharif, rabi, zaid
1960s
Green Revolution begins
High-yield wheat; Punjab led
Photosynthesis
Rule in one line: in light, leaves make glucose from CO2 and water and give off oxygen.
KEY TERM
Photosynthesis
Green plants make glucose from carbon dioxide and water. The energy comes from sunlight, trapped by the green pigment chlorophyll. Oxygen is given off. This happens in the chloroplasts of leaf cells, so leaves are the food factories of the plant. Extra glucose is stored as starch.
6CO2 + 6H2O→sunlight + chlorophyll→C6H12O6 + 6O2
| Needed | Comes from |
|---|---|
| Carbon dioxide | Air, entering through stomata |
| Water | Soil, taken up by roots and carried up the xylem |
| Sunlight | The sun |
| Chlorophyll | Chloroplasts in leaf cells; has magnesium at its centre |
QUICK FACT
To test a leaf for starch, boil it in alcohol to remove the chlorophyll. Then add iodine: it turns blue-black. A leaf kept in the dark for two days gives no blue-black colour. This shows that light is needed.
QUICK CHECK
PYQ · PPSC OHE 2016 — Chlorophyll is a naturally occurring compound in which the central metal is:
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Answer: D — Magnesium
A magnesium ion sits at the centre of the chlorophyll ring. Iron is at the centre of haemoglobin.
QUICK CHECK
PYQ · Punjab Police SI 2016 — It is not advisable to sleep under a tree at night because of the
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Answer: D — release of carbon dioxide
At night only respiration goes on, so the tree gives off carbon dioxide. Plants do not give off carbon monoxide.
Plant nutrition beyond photosynthesis
Rule in one line: pulses get nitrogen from bacteria living in their root nodules.
| Mode | What it means | Example |
|---|---|---|
| Parasitic | Takes food from a living host plant | Cuscuta (amarbel) |
| Insectivorous | Traps insects for extra nitrogen | Pitcher plant, Venus flytrap |
| Saprophytic | Absorbs food from dead matter | Mushrooms (fungi) |
| Symbiotic | Two organisms live together and both gain | Lichen (alga + fungus); Rhizobium in pulses |
QUICK CHECK
PYQ · Punjab Police SI 2023 — Where can you find nitrogen fixing bacteria?
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Answer: C — In the root nodules of legumes
Rhizobium lives in the root nodules of legumes such as gram, pea, moong and groundnut. Bamboo is a grass and has no such nodules.
QUICK CHECK
PYQ · Punjab Police Constable 2025 — Which of the following plant families are the major sources of Pyrrolizidine Alkaloids (PAs)?
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Answer: A — Boraginaceae, Asteraceae, and Fabaceae
Most plants known to make PAs belong to the borage, daisy and pea families.
Crop seasons
Rule in one line: kharif is sown with the monsoon; rabi is sown with the winter.
| Season | Sown | Harvested | Crops |
|---|---|---|---|
| Kharif (sauni) | June–July | September–October | Paddy, maize, cotton, bajra, groundnut, soybean |
| Rabi (hari) | October–November | March–April | Wheat, gram, pea, mustard, barley |
| Zaid | March | June | Watermelon, cucumber, moong |
QUICK FACT
Kharif crops need heat and plenty of water. Rabi crops need a cool season to grow and a warm, dry spell to ripen. Zaid crops are short summer crops grown between the two.
QUICK CHECK
PYQ · PPSC APRO 2016 — Which of the following is a Kharif crop?
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Answer: B — Maize
Maize is sown with the monsoon. Wheat, gram and barley are rabi crops.
QUICK CHECK
PYQ · PSSSB Patwari 2021 — Which of the following are NOT grown in the Kharif season in Punjab?
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Answer: C — Barley and mustard
Barley and mustard are rabi crops, sown in October–November. The other pairs grow in the monsoon season.
Farming practices and cropping patterns
Rule in one line: plough first; then sow, feed, water, weed, harvest and store.
STEPS OF CROP PRODUCTION
- 1Preparing the soilPloughing loosens and turns the soil to the needed depth. Levelling stops water loss.
- 2SowingGood seeds are sown at the right depth, often with a seed drill.
- 3Manure and fertiliserPut back the nutrients that crops take from the soil.
- 4IrrigationWells, canals and tube-wells; sprinkler and drip systems save water.
- 5WeedingWeeds are removed by hand or with weedicides such as 2,4-D.
- 6Harvest and storageA combine cuts and threshes; grain is dried and kept in silos and granaries.
| Pattern | What it means | Example |
|---|---|---|
| Monocropping | Only one crop on the same land, year after year | Cotton on the same field every year |
| Mixed cropping | Two or more crops sown together, mixed in one field | Wheat + gram; wheat + mustard |
| Intercropping | Two or more crops together in set rows | Soybean + maize |
| Crop rotation | Different crops one after another on the same land | Wheat, then moong |
| Catch crop | A short crop in the gap between two main crops | Summer moong after wheat |
| Relay cropping | The next crop is sown before the first is harvested | — |
QUICK CHECK
PYQ · Punjab Police Constable 2021 — The most essential operation for making the soil loose and porous to a desired depth as per requirement of the crop is _____.
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Answer: B — Ploughing
Ploughing is the first, main tillage. It loosens the soil to the depth the roots need. Harrowing and clod crushing only finish the surface.
QUICK CHECK
PYQ · Punjab Police Constable 2021 — Which cropping refers to growing of only one crop on the same piece of land year after year?
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Answer: D — Monocropping
Monocropping means one crop, the same land, every year. It drains the same nutrients and lets pests build up.
QUICK CHECK
PYQ · Punjab Patwari 2016 — A short duration crop in between two main seasonal crops is termed as:
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Answer: D — catch crop
A catch crop 'catches' the short gap between two main crops, such as summer moong after wheat. An inter crop grows alongside the main crop.
QUICK CHECK
PYQ · PPSC OHE 2016 — The nitrogenous supply of the soil is maintained when _____ is alternated with other crops.
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Answer: A — Moong
Moong is a pulse. Rhizobium in its root nodules fixes nitrogen, so rotating it with cereals restores soil nitrogen.
Crop protection, Bt cotton and ripening
Rule in one line: know the pest by its crop — pink bollworm attacks cotton.
KEY TERM
Bt cotton
Bt stands for Bacillus thuringiensis, a soil bacterium. A gene from it is put into the cotton plant. The plant then makes a protein that kills bollworm caterpillars that eat it. Such a plant with a gene from another organism is called transgenic (genetically modified).
Bt bacterium gene→Cotton plant→Toxic to bollworm
QUICK FACT
Ethylene is a plant hormone and a gas. Ripening fruit gives it off. Ripening chambers use ethylene gas to ripen green bananas and mangoes evenly. Using calcium carbide, which gives off acetylene, is unsafe and banned for this.
QUICK CHECK
PYQ · Punjab Police Constable 2025 — Pink bollworm (Gulabi Sundi) is a major pest that affects which of the following crops?
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Answer: C — Cotton
The pink bollworm larva bores into cotton bolls and spoils the lint and seed. It is a major pest in the Malwa cotton belt.
QUICK CHECK
PYQ · PPSC DSSO 2018 — Consider the following statements. I. In Bt cotton a transgenic plant Bt refers to Clostridium thuringiensis. II. The Bt gene is derived from a fungi. III. Nematode resistant transgenic cotton has been produced by inserting Bt gene. Which of the statement(s) given above is/are correct?
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Answer: D — None of these
All three are wrong. Bt is Bacillus (not Clostridium), a bacterium (not a fungus), and its gene protects against insects like bollworm, not nematodes.
QUICK CHECK
PYQ · Punjab Police SI 2016 — The gas used for artificial ripening of green fruit is
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Answer: A — ethylene
Ethylene is the fruit's own ripening hormone. Acetylene from calcium carbide also ripens fruit, but it is harmful and illegal.
Farm revolutions and animal husbandry
Rule in one line: each 'revolution' is a big jump in one farm product — learn the colour with the product.
| Revolution | Product | Linked names |
|---|---|---|
| Green | Food grains, mainly wheat | M. S. Swaminathan (India); Norman Borlaug (high-yield wheat) |
| White | Milk | Verghese Kurien; Operation Flood |
| Blue | Fish (aquaculture) | — |
| Yellow | Oilseeds | — |
| Golden | Horticulture (fruits) and honey | — |
| Round | Potato | — |
| Grey | Fertilisers | — |
| Silver | Eggs (poultry) | — |
KEY TERM
The Green Revolution
From the mid-1960s, India used high-yielding varieties (HYV) of wheat and rice, with irrigation, chemical fertilisers and pesticides. Grain output rose fast, and Punjab led the change. It worked best for wheat. Crop insurance was not part of this package.
HYV seeds→Irrigation→Fertilisers→More grain
QUICK CHECK
PYQ · Punjab Election Kanungo 2021 — Who is the originator of the 'Green Revolution' in India?
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Answer: B — MS Swaminathan
M. S. Swaminathan led the Green Revolution in India. Borlaug bred the high-yield wheat and is called the father of the Green Revolution worldwide. Punjab Excise Inspector 2018 asked the same question.
QUICK CHECK
PYQ · PPSC OHE 2016 — Who is known as the ‘Father of White Revolution’?
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Answer: A — V Kurien
Verghese Kurien led Operation Flood through Amul and the National Dairy Development Board. India became the world's largest milk producer.
QUICK CHECK
PYQ · PPSC EO 2018 — Consider the following: 1. Yellow Revolution – Eggs 2. Golden Revolution – Oilseeds 3. Round Revolution – Potato 4. Grey Revolution – Fertilizers. Which of the above is/are correctly matched?
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Answer: B — 3 and 4
Round = potato and Grey = fertilisers are right. Yellow is oilseeds and Golden is horticulture and honey, so 1 and 2 are wrong. PPSC SSO 2018 repeated it.
| Area | What it means | Notes |
|---|---|---|
| Dairy (cattle) | Rearing cows and buffaloes for milk | Murrah buffalo; Sahiwal and Red Sindhi cows |
| Poultry | Rearing hens | Layers give eggs; broilers give meat |
| Apiculture | Rearing honey bees | Honey and wax |
| Pisciculture | Rearing fish | Rohu, catla in ponds |
| Sericulture | Rearing silkworms | Silk from cocoons |
More facts that are asked once in a whileTap to open
- Loss of water vapour from leaves is transpiration. It cools the plant and pulls water up.
- Soybean is both a pulse (legume) and an oilseed crop.
- Hydroponics is growing plants in nutrient-rich water, without soil.
- Rice was the first crop plant whose genome was sequenced.
- The age of a tree can be found by counting its annual rings.
- Neem leaves are kept with stored grain to keep insects away.
- Drip irrigation gives water drop by drop at the roots. It suits fruit trees and dry areas.
Traps and practice
Last revision — where the options try to fool you.
COMMON TRAPS
- Chlorophyll has magnesium; haemoglobin has iron.
- At night trees give off carbon dioxide, not carbon monoxide.
- Nitrogen-fixing bacteria live in the root nodules of legumes, not in leaves.
- Maize, paddy, cotton are kharif; wheat, barley, mustard, gram are rabi.
- Monocropping = one crop every year; catch crop = short crop between two main crops.
- Bt is a bacterium (Bacillus), not a fungus; Bt cotton fights bollworm.
- Fruit is ripened with ethylene, not ethane or acetylene.
- Green = grain, White = milk, Blue = fish, Yellow = oilseeds, Round = potato, Grey = fertilisers.
CHECK YOURSELF
Why is it good to grow moong between two cereal crops?
Show answer
Moong is a pulse. Rhizobium in its root nodules fixes nitrogen from the air. So the soil gets nitrogen back and less urea is needed.
FLASHCARDS
Plant and crop flashcards
- Metal in chlorophyll
- Magnesium
- Pores on leaves
- Stomata
- Nitrogen-fixing bacterium of pulses
- Rhizobium
- Parasitic plant
- Cuscuta (amarbel)
- Pest of cotton
- Pink bollworm
- Fruit-ripening gas
- Ethylene
- Green Revolution in India
- M. S. Swaminathan
- White Revolution
- Verghese Kurien
QUICK BYTES
- 6CO2 + 6H2O → C6H12O6 + 6O2, with sunlight and chlorophyll
- Chlorophyll: magnesium; starch test: iodine turns blue-black
- Rhizobium in root nodules of legumes
- Kharif: paddy, maize, cotton; rabi: wheat, barley, mustard
- Ploughing loosens soil; catch crop fills the gap
- Bt = Bacillus thuringiensis; pink bollworm = cotton
- Green: Swaminathan; White: Kurien
- PAs: Boraginaceae, Asteraceae, Fabaceae