GCE O/L past paper Questions and Answers from 1999 to 2017 will be uploaded very soon. The questions and answers are arranged topic wise.
Q. Describe how energy from the sun is trapped by plants and is eventually used for a person to move their arm.
The energy from the sun reached the ecosystem in the form of light. A green pigment called chlorophyll present in the plant cells trap this energy and used to convert carbon dioxide and water to carbohydrate and stored as starch. This process is called photosynthesis. Thus by photosynthesis green plants convert sunlight energy into chemical energy. When a person eats the green vegetables, the starch is digested in his alimentary canal into glucose. The glucose is then absorbed into the blood through the wall of the small intestine and carried in blood to the muscle cells, where it is used in respiration to release energy. This energy is used for muscle contraction to move his arm.
Q.State what is meant by transpiration?
Transpiration is the loss of water vapour from the aerial parts of a plant through the stomata.
Q.Explain how the transpiration stream is important for the production of proteins in a plant.
Transpiration stream brings nitrates dissolved in water from the soil. These nitrates combine with carbohydrate to form amino acids. Amino acids are used to synthesis protein.
Q. Describe and explain how tissues in the stem of a plant become stained when a plant is carefully removed from the soil and placed in a solution of dye for a few hours.
The dye diffuses through the permeable cell wall of the root hair cells. The dye reaches the root xylem and then travel upwards due to the transpiration pull.
Q.Describe the functions of the kidneys.
Kidney is an excretory organ. It filters the urea, water and other toxic substances from the blood and form urine. Kidney helps in osmoregulation. It regulates the amount of water and salts in the body fluids. Kidney removes hormones after their effect on the target organs.
Q. Describe and explain the ways in which a person may be kept alive even when both of their kidneys have stopped functioning.
The person may be kept alive by dialysis. In dialysis the blood is taken from the vein of the person and passes along a coiled partially permeable tube. The tube is surrounded by a dialysis fluid. The concentration of the dialysis fluid must be same as that of the blood except urea and other waste materials. The urea and other waste materials are diffused out of the blood. The dialysis fluid is continuously changed and the temperature of the dialysis fluid should be same as body temperature. The cleaned blood is returned to the vein of the person through a bubble trap. Kidney transplant is another way to keep the person alive. But difficulty in getting a donor, less facilities in hospitals, less experts in this field etc. limit the kidney transplant.
Q. Define the term drug.
A drug is an externally administered chemical substance which modifies the metabolism in the body.
Q.Describe the possible effects of the abuse of a named drug.
Heroin is a drug which is normally abused. It is a powerful depressant. It removes anxiety and creates a feeling of well being.
Heroin is a drug to which body shows tolerance. Its dosage must be progressively increased to get the same effect.
Heroin is an addictive drug. The physical dependence on a drug is called addiction. The addicts cannot do any work without their normal dose.
Addiction of heroin makes the user to lead a criminal life to make money to buy the drug.
Heroin is an injectable drug. Many drug addicts share un sterilized the needles and syringes. So that the chances of contracting blood born diseases are more.
Heroin causes withdrawal symptoms such as vomiting, shaking, hallucination etc
Q. Explain what is meant by a hormone.
A hormone is a chemical substance, produced by a gland, carried by the blood, which alters the activity of one or more specific target organs and is then destroyed by the liver.
Q.Give an example of a hormone and describe how it is involved in maintaining constant conditions within the human body.
Insulin is a hormone produced by the pancrease in human.
Insulin regulates the blood glucose level.
The normal blood glucose level of a healthy person is 80 – 100 mg /100 cm3 of blood. After a heavy meal, the blood glucose level rises. The brain detects this change and stimulates the pancreas to produce insulin. Insulin stimulates the liver cells to convert excess glucose into glycogen. Thus when a deviation from a set point occurs in the body an automatic response is taken to return to the set point, this is called homeostasis.
Q.Describe the characteristics of bacteria.
Bacteria are microscopic unicellular organisms. They have cell wall, cell membrane and cytoplasm. Nucleus is absent but a DNA is present in the cytoplasm. Some bacteria are parasitic and cause diseases in animals and plants. Most of the bacteria are saprophytic.