Ch20 Photosynthesis

Question 1

Adaptive features of leaves for photosynthesis

Answer 1

The leaf blade is often broad and flat to provide a large surface area for absorbing sunlight
The leaf is thin to allow gases and light to reach the photosynthetic cells easily
The leaves are arranged in a way that there is little overlapping among the leaves. This allows each leave to expose to maximum amount of sunlight.

Question 2

Internal structure of the leaf

Answer 2

Palisade mesophyll consist of tightly packed cells that contain many chloroplasts and located on the upper side of leaf. This allows effective absorption of sunlight.
Spongy mesophyll consist of loosely packed cells with many airspace. The cells contain chloroplast this allows gases to diffuse freely inside the leaf and for absorption of sunlight.
Upper and lower epidermis are covered by a thin layer of waxy cuticle. This reduces water loss so the water is kept inside for photosynthesis.
Stoma is surrounded by a pair of guard cells that contain chloroplast . This opens or closes under different condition to regulate the passage of gases and water vapour
Vascular bundle is made up of xylem and phloem. This allows efficient transport of materials into and away from the leaf and support and spread the leaf blade.

Question 3

Features of chloroplast for photosynthesis

Answer 3

A chloroplast is bounded by a double membrane and it is filled with a jelly like fluid called stroma. Stroma have enzymes starch grains and other photosynthetic products. A network of dislike membranous sacs called thylakoids is suspended in the stroma. The thylakoids are arranged in stacks called Grana. Chlorophyll is located on the thylakoid membrane. The grana are interconnected by extensions from the thylakoids. This allows efficient transport of photosynthetic products. A chloroplast has about 50 grana each consisting of about 50 thylakoids. This provides a large surface area to pack more chlorophyll for absorbing light 

Question 4

What does nature of science requires?

Answer 4

Creativity and imagination

Question 5

Photochemical reactions

Answer 5

Occurs in the thylakoid of chloroplast. Chlorophyll absorbs light energy. The excited electron is passed through the electron transport chain. The energy released is used for photophosphorylation. ADP combines with phosphate to form ATP. Light energy is converted to chemical energy. In photolysis, water splits to form hydrogen and oxygen. Hydrogen is accepted by NADP to form NADPH. Oxygen gas is released as by-product.

Question 6

Carbon fixation: Calvin cycle

Answer 6

Occurs in stroma of chloroplast. Under the action of enzymes, carbon dioxide combines with one molecules of 5-C compound.
Using energy from ATP and hydrogen from NADPH, the 3-C compound is reduced to triose phosphate. Triose phosphate are used to regenerate the original 5-C compound So that Calvin cycle can repeat itself. This uses energy from ATP.
TWO MOLECULES OF TRIPHOSPHATE COMBINES TO FORM ONE MOLECULES OF GLUCOSE.

Question 7

The fate of photosynthetic products

Answer 7

Triose phosphate is quickly synthesised into glucose or fructose. Glucose and fructose combined to form sucrose for transport to non-photosynthetic tissues through the phloem. Sucrose is a suitable form for transport, because it is soluble, but relatively inactive. Excess glucose is quickly built into starch and stored in cells. Starch is suitable form for storage because it is insoluble and can be stored in leaves without affecting the water potential of the leaves. Some glucose is cellulose and is the major component of cell walls. Starch can be broken down to form glucose which can be used as an energy source or used to make cellulose. May also convert to sucrose for transport. Metabolic intermediates can be used to synthesise glycerol and fatty acid ,glycerol and fatty acid can combine to form lipids , lipids may be stored as an energy reserve in some plants.  intermediate of glucose breakdown may combined with an inorganic ions to form amino acid, which are building blocks of protein.

Question 8

What is limiting factor?

Answer 8

Limiting factor slows down the rate of photosynthesis, if its supply is less 

Question 9

Different temperature affecting the activity of enzymes

Answer 9

At low temperature enzymes are inactivated
At high temperature enzymes are denatured