CELL PHYSIOLOGY NOTES
By the end of the topic, the learner should be able to:
Meaning of cell physiology
The term physiology refers to the functions that occur in living organisms.
Cell physiology refers to the process through which substances move across the cell membrane.
Several physiological processes take place inside the cell e.g. respiration.
Oxygen and glucose required enter the cell while carbon (IV) oxide and water produced leave the cell through the cell membrane.
Structure and properties of cell membrane
Properties of cell membrane
An increase in the concentration of molecules at one region results in a steeper concentration gradient which in turn increases the rate of diffusion.
High temperature increases kinetic energy of molecules. They move faster hence resulting in an increase in rate of diffusion, and vice versa.
Size of Molecules or Ions
The smaller the size of molecules or ions, the faster their movement hence higher rate of diffusion.
The denser the molecules or ions diffusing, the slower the rate of diffusion, and vice versa.
The medium through which diffusion occurs also affects diffusion of molecules or ions. For example, diffusion of molecules through gas and liquid media is faster than through a solid medium.
This refers to the thickness or thinness of surface across which diffusion occurs. Rate of diffusion is faster when the distance is small i.e., thin surface.
Surface Area to Volume Ratio
The larger the surface area to volume ratio, the faster the rate of diffusion.
For example, in small organisms such as Amoeba the surface area to volume ratio, is greater hence faster diffusion than in larger organisms.
Factors Affecting Diffusion
Role of Diffusion in Living Organisms
Some processes that depend on diffusion include the following:
Factors Affecting Osmosis
Size of solute molecules-
Osmosis' occurs only when solute molecules are too large to pass through a semi-permeable membrane.
Osmosis occurs when two solutions of unequal solute concentration are separated by a semi-permeable membrane.
High temperatures increase movement of water molecules hence influence osmosis. However, too high temperatures denature proteins in cell membrane and osmosis stops.
Increase in pressure affects movement of water molecules.
As pressure increases inside a plant cell, osmosis decreases.
Roles of Osmosis in Living Organisms
The following processes depend on osmosis in living organisms:
Water Relations in Plant and Animal Cells
Water Relations in Plants and Animals
Factors Affecting Active Transport:
Availability of carbohydrates
Role of Active Transport in Living Organisms
Processes requiring active transport:
1. Experiment to Demonstrate Diffusion
4. Experiment to Demonstrate Turgor and Plasmolysis in Onion Epidermal Cells
CELL PHYSIOLOGY QUESTIONS
1. 1994 Q6 P1
Give a reason for each of the following
a) A mature plant cell does not lose its shape even after losing water.
b) Xylem vessels do not collapse even when they do not contain water.
2. 1995 Q4 P1
Explain what would happen to red blood cells if they are placed in a concentrated salt solution ( 2 marks)
3. 1995 Q10 P1
An experiment was carried out to investigate the rate of reaction shown below
Sucrose →Fructose + Glucose
For the products fructose and glucose to be formed, it was found that substance K was to be added and the temperature maintained at 370C. When another substance L was added, the reaction slowed down and eventually stopped.
(a) Suggest the identify of substances K and L (2 marks)
(b) Other than temperature state three ways by which the rate of reaction could be increased (3 marks)
(c) Explain how substance L slowed down the reaction (2 marks)
4. 2000 Q8 P1
Why is oxygen important in the process of active transport in cells?
5. 2004 Q16 P1
a) What is diffusion (2 marks)
b) How do the following factors affect the rate of diffusion?
i) Diffusion gradient (1 mark)
ii) Surface area volume ratio (1mark)
iii) Temperature (1mark)
c) Outline three roles of active transport in the human body (3 marks)
6. 2005 Q7 P1
State the importance of osmosis in plants. (3 marks)
7. 2009 Q13 P1
(a) Distinguish between diffusion and active transport (2 marks)
(b) State one role that is played by osmosis in (1 mark)
8. 2010 Q7 P1
Distinguish between haemolysis and plasmolysis. (2 marks)
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