1(a) How are the cardiac muscles adapted to their function? Any 6@ 01½ = 09
Cardiac muscles are the muscles which make up the wall of the heart. These muscles contain fibres made up of myofibrils consisting of actin and myosin filaments. This accounts for the stripped appearance of the muscle fibres.
The muscles are richly supplied with blood capillaries to ensure sufficient supply of oxygen and nutrients.
Mitochondria are well supplied to ensure sufficient energy production and supply for pumping activity of the heart.
The striations make it tough and strong to withstand the pumping activity of the heart as it confronts the blood pressure.
The muscles are able to oxidize lactic acid from skeletal muscles for energy release. This allows them to work efficiently even when oxygen supply is limited.
The branching system of the muscles ensures its uniform excitation, thus regular heart beats are produced.
The contraction of the muscle is slower than in the skeletal muscles. This prevents muscle fatigue and so the muscle can work continuously without stopping.
The actin and myosin filaments contained assist the contraction of the muscle because they are extensible proteins.
It has many collagen fibres which increase the strength of the muscle contraction.
Cardiac strokes are self-generated, so it is not richly supplied with the neurons.
These adaptations enable the heart to pump blood throughout life without getting fatigue or any tear.
(b) Basing on Potassium theory explain how control of opening and closing of stomata is attained.
@ 01½ = 06
Opening of stomata; during the day blue light from the sunlight activates the protein pump and ATP is broken to ADP and Pi. Energy is used by H+ pump to pump out H+ of the guard cells. This establishes an electrochemical gradient that allow K+ ions to enter into guard cells by way of channel protein.
Accumulation of K+ ions inside the guard cells cause drop of water potential lower than that of the surrounding cells, and water moves in by osmosis. The guard cells become turgid hence stomata open.
Closing of stomata; during dark, H+ pump is inactivated, while K+ ions move out of the guard cells following the concentration gradient.
Loss of K+ ions causes a rise in water potential higher than that of the surrounding cells, and water moves out by osmosis. The guard cells become flaccid and hence stomata close.
Total = 15 Marks
With an aid of diagram describe the structure of stomata.
Stomata are openings on the surface of the leaves. Stomata consist of a pair of specialized epidermal cells, guard cells, which surround a small pore known as stomata aperture.
Guard cell is differentiated from epidermal cell by being kidney shaped. Unlike other epidermal cells, they possess chloroplasts and have denser cytoplasm with a more prominent nucleus.
The inner wall of guard cell is thicker and less elastic than outer one. These cells control opening and closing of stomata.
It is through stomata that plants exchange gases with the environment and lose excess water by transpiration. = 10
Diagram = 02
Caption = 00½
Labeling, any 5 @ 00½ = 02½
Caption; A labelled diagram of stomata
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