Chapter 6 igcse book biolgy ,learning ,science ,biolgy ,igcse ,english ,learning ,science ,biolgy ,igcse ,english ,learning ,science ,biolgy ,igcse ,english ,learning ,science ,biolgy ,igcse ,english ,learning ,science ,biolgy ,igcse ,english ,learning ,science ,biolgy ,igcse ,english

1. PLANT NUTRITION

2. Nutrition : taking in useful substances.
★ Most of the plants make their own food. They use simple inorganic
substances from the air and soil.
★ Plants build these substances into complex materials.
★ Substances made by living things are said to be organic.

3. Photosynthesis

4. Photosynthesis : ‘Photo’ means light, and ‘synthesis’ means manufacture.
★ The process of photosynthesis occurs when green plants use the energy of
light to convert carbon dioxide and water into carbohydrates.
★ During photosynthesis: Light energy is absorbed by chlorophyll, a green
substance found in chloroplasts in some plant cells.
★ Absorbed light energy is used to convert carbon dioxide and water into a
sugar called glucose. Oxygen is released as a by-product.

5. ★ Photosynthesis can only occur when a plant has access to water, carbon
dioxide, sunlight and chlorophyll.
★ Plant cells naturally produce chlorophyll, and they draw carbon dioxide
directly from the air. Water and sunlight must be acquired from external
sources.

7. Leaves - Leaf Structure
● A leaf is a factory for making carbohydrates. (photosynthesis)
epidermis - the protective, outer layer of cells on the surface of a leaf. The guard cells (and stoma) are
part of the epidermis. The surface of many leaves is coated with a waxy cuticle which is secreted by the
epidermis.
cuticle - the waxy, water-repelling layer on the outer surface of a leaf that helps keep it from dying out The
cuticle is secreted by the epidermis and is often thinner on the underside of leaves. The cuticle is
generally thicker on plants that live in dry environments.
stoma - (plural stomata) a pore (or opening) in a plant's leaves where water vapor and other gases leave
and enter the plant. Stomata are formed by two guard cells that regulate the opening and closing of the
pore. Generally, many more stomata are on the bottom of a leaf than on the top.

10. vein - Veins provide support for the leaf and transport both water and minerals (via xylem) and food
energy (via phloem) through the leaf and on to the rest of the plant.
palisade mesophyll - a layer of elongated cells located under the upper epidermis. These cells contain
most of the leaf's chlorophyll, converting sunlight into usable chemical energy for the plant.
spongy mesophyll - the layer below the palisade mesophyll; it has irregularly-shaped cells with many air
spaces between the cells. These cells contain some chlorophyll. The spongy mesophyll cells
communicate with the guard cells (stomata), causing them to open or close, depending on the
concentration of gases.

11. Leaf Adaptations
Carbon dioxide : The carbon dioxide can get into the leaf through stomata by diffusion.
There is an air space behind each stoma which
connects with other air
spaces between the spongy mesophyll cells.
The carbon dioxide can therefore diffuse to all
the cells in the leaf.
! only 0.04% of the air is carbon dioxide.

12. Water : Water is absorbed by the root hairs from the soil and carry up to the leaf in the xylem vessels.

13. Sunlight: Leaves have a large surface area so more light hits them.
The upper epidermis of the leaf is transparent, allowing light to enter the leaf.
The palisade cells contain many chloroplasts which allow light to be converted into energy by the leaf.

14. Uses of Glucose
● Used for energy
● Stored as starch
● Used to make proteins and other organic substances
● Changed to sucrose for transport

15. Used for energy
● Glucose is used in respiration to release energy.

16. Stored as starch
● Glucose is a simple sugar and can dissolve in water. It is also a reactive
substance.
● Glucose is not a very good for storage.
Because;
➔ it might get involved in chemical reactions where it is not wanted.
➔ it would dissolve in water in a plant cell and might be lost from the cell.
➔ when dissolved, it would increase the concentration of the solution in the cell,
which could cause damage.

17. ★ The glucose is converted into starch to be stored. Starch is not very reactive and not very soluble in
water.

18. Used to make proteins and organic substances
● Glucose and starch can be converted into other substances in plants. For example:
➔ Cellulose for cell walls
➔ Proteins for growth and repair
➔ Chlorophyll for photosynthesis
★ To do protein ; plants need nitrogen. They absorb nitrate ions from the soil. The nitrate
ions combine with glucose to make amino acids. The amino acids are binding together
to form protein molecules.
★ To do chlorophyll ; plants need nitrogen and magnesium. The magnesium is also
obtained from the soil.

19. Changed to sucrose for transport
● Sucrose molecules are soluble and less reactive than glucose.
● Sucrose dissolve in the sap in the phloem vessels and can be transported to
whichever parts of the plant need them.
★ Sucrose can turned back into glucose, to be broken down to release energy,
turned into starch for store or used to make other substances.

20. Limiting Factors
● Several factors can affect the rate of photosynthesis:
➔ light intensity
➔ carbon dioxide concentration
➔ temperature

21. Light intensity
● Light is absorbed by chlorophyll,
which convert the radiant energy into
chemical energy (ATP)
● As light intensity increases reaction
rate will increase, as more chlorophyll
are being photo-activated
● At a certain light intensity
photosynthetic rate will plateau, as all
available chlorophyll are saturated
with light.

22. Carbon dioxide concentration
● Carbon dioxide is involved in
the fixation of carbon atoms to
form organic molecules
● As carbon dioxide
concentration increases
reaction rate will increase, as
more organic molecules are
being produced
● At a certain concentration of
CO2 photosynthetic rate will
plateau, as the enzymes
responsible for carbon fixation
are saturated

23. Temperature
● The chemical reactions that combine
carbon dioxide and water to produce
glucose are controlled by enzymes.
As with any other enzyme-controlled
reaction, the rate of photosynthesis is
affected by temperature.
● At low temperatures, the rate of
photosynthesis is limited by the
number of molecular collisions
between enzymes and substrates. At
high temperatures, enzymes are
denatured.