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Unit 1: Photosynthesis and the carbon cycle

More about photosynthesis — HIA International - Grade 8 Revision Notes & Topical Questions

5 min read 8 parts Lesson 3 of 5 3 quizzes

📚 HIA International - Grade 8 Hub / Topical Revision
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Lesson summary

More about photosynthesis — HIA INTERNATIONAL notes: Explain where photosynthesis happens in a plant, how a leaf is adapted for it and why plants need magnesium and nitrate.Chlorophyll — it is kept inside chloroplasts, which capture energy from sunlight.Where — photosynthesis hap…

  • Variegated leaf
  • Waxy layer
  • Upper epidermis
  • Palisade layer
  • Spongy layer
  • Lower epidermis

Section 1 of 8Chloroplasts and chlorophyll

Chlorophyll
  • Chlorophyll it is kept inside chloroplasts, which capture energy from sunlight.
Where
  • Where photosynthesis happens inside chloroplasts, and not every plant cell has them.
Leaves
  • Leaves the cells in leaves have the most chloroplasts.
Storage
  • Storage on sunny days plants make more carbohydrate than they use, and store it as starch inside the chloroplasts.

Section 2 of 8Testing a leaf for starch

1
Destarch the plant by keeping it in the dark for 48 hours, then put it in light.
2
Drop a leaf into boiling water for about 2 minutes to break the cell membranes.
3
Turn off the burner, because ethanol is flammable.
4
Put the leaf in ethanol in a test tube standing in hot water to remove the green colour.
5
Dip the brittle leaf in warm water to soften it and spread it on a tile.
6
Add iodine solution; blue-black areas contain starch.
Variegated leaf
  • Variegated leaf only the green parts turn blue-black, so chlorophyll is needed.
Covering part of a leaf with foil shows that light is needed.

Section 3 of 8Inside a leaf

Thin leaf
  • Thin leaf sunlight reaches the cells easily and gases have a short distance to diffuse.
Waxy layer
  • Waxy layer on the surface it stops the leaf cells drying out.
Upper epidermis
  • Upper epidermis it protects the cells inside the leaf.
Palisade layer
  • Palisade layer its cells do most of the photosynthesis.
Spongy layer
  • Spongy layer it has many air spaces and does a small amount of photosynthesis.
Veins
  • Veins they carry water to the cells in the leaf (xylem) and take sugars away (phloem).
Lower epidermis
  • Lower epidermis it protects the cells and contains the stomata.

Section 4 of 8Gas exchange through stomata

Stomata
Stomata tiny holes (singular stoma) in the lower epidermis.
Carbon dioxide
  • Carbon dioxide it diffuses in from the air through the stomata and the air spaces between cells.
Oxygen
  • Oxygen it diffuses out of the leaf through the stomata.
Guard cells
  • Guard cells they open and close the stomata.
Test
  • Test a leaf in warm water gives off bubbles, mostly from the lower surface where there are most stomata.

Section 5 of 8Minerals for plant growth

MineralWhy the plant needs itShortage
MagnesiumNeeded to make chlorophyllLeaves look yellow, and less photosynthesis happens
NitrateSupplies nitrogen to convert carbohydrates to proteins and to make chlorophyllLeaves die and the plant stays small

Section 6 of 8Fertilisers

Fertiliser
  • Fertiliser it contains minerals that make crops grow larger and give a higher yield.
Yield
Yield the quantity of crop that the farmer harvests.
Source
  • Source plants take minerals from the soil through their roots, but soil may lack some.
Soil tests
  • Soil tests farmers test soil to find which minerals are lacking and where to add fertiliser.

Section 7 of 8Key terms

TermMeaning
ChloroplastThe part of a plant cell that contains chlorophyll and carries out photosynthesis.
StomataTiny holes in the lower epidermis of a leaf.
FertiliserA substance containing minerals added to soil to improve crop growth.
YieldThe quantity of crop harvested.
StarchThe carbohydrate in which plants store glucose.
Palisade layerThe leaf layer whose cells do most of the photosynthesis.
Limiting factorThe factor in shortest supply that limits the rate of photosynthesis.

Section 8 of 8Exam technique

1
Photosynthesis happens in all plant cells — it happens only in cells with chloroplasts.
2
Carbon dioxide enters through the roots — it enters through the stomata in the leaves.
3
Plants take in nitrate for energy — nitrate gives nitrogen to make proteins and chlorophyll.
4
A starch test works on a green leaf straight away — the leaf must be boiled and the chlorophyll removed first.

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