WAEC SSCE - Biology - 1989
Question 1 Report
The cell membrane consists of
Answer Details
The cell membrane is a thin, flexible layer that surrounds the cells of all living organisms. It separates the inside of the cell from the outside environment and regulates the movement of substances in and out of the cell. The cell membrane is primarily composed of two types of molecules: lipids and proteins. The most common type of lipid in the cell membrane is phospholipids. They have a hydrophilic (water-loving) head and a hydrophobic (water-hating) tail. The phospholipids are arranged in a bilayer with the hydrophilic heads facing outward and the hydrophobic tails facing inward. The proteins in the cell membrane have a variety of functions, such as transporting molecules across the membrane, serving as receptors for chemical signals, and anchoring the membrane to the cell's cytoskeleton. Carbohydrates are also present in the cell membrane, but they are attached to the surface of the lipids and proteins, forming glycolipids and glycoproteins. They play a role in cell-to-cell recognition and communication. Therefore, the correct option is (C) lipids and proteins, as they are the main components of the cell membrane, while carbohydrates are also present but in a minor proportion.
Question 2 Report
The term used in describing the effective management of national resources by man is
Answer Details
The term used in describing the effective management of national resources by man is conservation. Conservation refers to the sustainable use and management of natural resources such as water, forests, wildlife, and minerals. It involves balancing the needs of humans with the needs of the environment, to ensure that natural resources are not depleted or destroyed over time. Conservation aims to protect the environment and the natural resources it provides, while also ensuring that these resources are used in a responsible and sustainable way. This can involve a range of strategies, such as setting aside protected areas for wildlife, implementing sustainable forestry practices, and developing renewable sources of energy. Conservation is an important concept in environmental science, as it recognizes the importance of preserving natural resources for future generations. By conserving natural resources, we can ensure that they will continue to be available for the benefit of all, while also protecting the environment and the many species that depend on it.
Question 3 Report
Which of the following constitutes the main internal tissue of a leaf?
Answer Details
The main internal tissue of a leaf is the mesophyll. The mesophyll is the primary site of photosynthesis in the leaf, where light energy is used to convert carbon dioxide and water into glucose and oxygen. The mesophyll tissue is located between the upper and lower epidermis of the leaf and consists of two distinct layers: the palisade mesophyll and the spongy mesophyll. The palisade mesophyll is made up of long, narrow cells that are densely packed with chloroplasts, which are the organelles responsible for photosynthesis. The spongy mesophyll, on the other hand, is made up of loosely packed cells that contain air spaces, which allow for the exchange of gases during photosynthesis. Vascular tissue, which consists of the xylem and phloem, is responsible for transporting water, minerals, and nutrients throughout the plant and is also present in the leaf. The upper and lower epidermis are the outermost layers of the leaf, which serve to protect the mesophyll tissue and regulate gas exchange through specialized pores called stomata. The cuticle is a waxy layer that covers the outer surface of the leaf and helps to prevent water loss.
Question 4 Report
Which of the following organisms is at the tissue level of organization?
Answer Details
Question 6 Report
Which of the following statements is not correct about food chains?
Answer Details
The statement that is not correct about food chains is: "There is no energy loss in a food chain." In reality, energy is lost as it moves through a food chain, and this is due to the second law of thermodynamics, which states that energy cannot be created or destroyed, but it can be converted from one form to another. As organisms consume other organisms in a food chain, they convert some of the energy they receive into other forms of energy, such as heat or movement, which are not available to be passed on to the next organism in the chain. This means that energy is lost at each stage of the food chain, and this loss of energy is one reason why food chains tend to be relatively short. The longer a food chain is, the more energy is lost, and the less efficient it becomes.
Question 7 Report
What is the name given to the structure labelled A at this stage of cell division?
Answer Details
The name given to the structure labelled A at this stage of cell division is "chromosome". Chromosomes are structures made up of DNA and proteins that carry an organism's genetic information. They are visible during cell division when the DNA condenses and becomes visible under a microscope. At this stage, each chromosome consists of two identical copies, called chromatids, that are held together at a region called the centromere. Chromosomes play a crucial role in cell division, as they ensure that each daughter-cell receives a complete set of genetic information. After cell division is complete, the chromosomes unravel into their chromatin form, which allows for normal cellular activities, such as gene expression, to take place.
Question 8 Report
Which of the following is not true about a bacterial colony growing on an agar plate?
Answer Details
Question 9 Report
One of the methods of preventing measles is by
Answer Details
The most effective way to prevent measles is by vaccinating young children. Measles is a highly contagious viral disease that spreads through the air when an infected person coughs or sneezes. Vaccination creates immunity in the body, which helps to protect against the virus. This means that if a person comes into contact with someone who has measles, they are less likely to become infected. Vaccination not only protects the individual who receives the vaccine, but also helps to prevent the spread of the disease within the community. Therefore, vaccinating young children is an important public health measure to prevent measles outbreaks.
Question 10 Report
Which of the following processes will not introduce carbondioxide into the atmosphere?
Answer Details
The process that will not introduce carbon dioxide into the atmosphere is photosynthesis. Photosynthesis is the process by which plants, algae, and some bacteria use sunlight to produce glucose from carbon dioxide and water. In this process, carbon dioxide is actually removed from the atmosphere and converted into organic matter. On the other hand, the other options listed involve the release of carbon dioxide into the atmosphere. Breathing, respiration, and putrefaction are all processes that involve the breakdown of organic matter, which releases carbon dioxide as a byproduct. Burning, whether it be of fossil fuels or biomass, also releases carbon dioxide into the atmosphere, contributing to the increase in atmospheric CO2 levels and climate change.
Question 11 Report
Over-crowding in seedlings of different species is less serious than over-crowding involving one species
because different species may
Answer Details
Overcrowding in plants can lead to competition for resources such as water, nutrients, and sunlight. When seedlings of different species are overcrowded, there is less competition for resources because the different species may have different nutritional needs or be active at different times. This means that each species can obtain the necessary resources to grow and develop without being hindered by the other species. On the other hand, when overcrowding involves one species, they will be in direct competition with each other since they have similar nutritional needs, and this can hinder their growth and development. Therefore, overcrowding in seedlings of different species is less serious than overcrowding involving one species.
Question 12 Report
Which of the following represents the phenotypic ratio, when a plant Rr is crossed with another plant Rr,
assuming that the gene R for round seed is dominant and wrinkled r is recessive?
Answer Details
The cross between a plant with genotype Rr (where R is the dominant allele for round seed and r is the recessive allele for wrinkled seed) and another Rr plant can be represented as follows: | | R | r | | - | - | - | | R | RR | Rr | | r | Rr | rr | The Punnett square above shows that the offspring can have the genotypes RR, Rr, or rr in a ratio of 1:2:1 respectively. Since the round seed trait is dominant, the plants with genotypes RR and Rr will have a round seed phenotype. Only the plants with genotype rr will have the wrinkled seed phenotype. Therefore, the phenotypic ratio of the offspring is 3:1 (round seed : wrinkled seed) as only one out of four possible outcomes has the recessive trait (wrinkled seed). Thus, option (D) represents the correct phenotypic ratio for this cross.
Question 14 Report
The part through which manufactured sugar is transported is labelled
Answer Details
Question 15 Report
The pilaferous layers is labelled
Question 16 Report
The part labelled VII is made up of
Question 18 Report
Blood in mammals transports oxygen because it contains the pigment called
Answer Details
The pigment that transports oxygen in the blood of mammals is called "haemoglobin". Haemoglobin is a protein molecule found in red blood cells that has a high affinity for oxygen. When oxygen enters the lungs, it binds to the haemoglobin molecules in the red blood cells and is transported throughout the body. As the oxygen-depleted blood returns to the lungs, the haemoglobin releases the oxygen, which is then exhaled. This cycle repeats with each breath, allowing oxygen to be transported to all the cells in the body that require it. The other options given, chlorocruorin, melanin, haemocyanin, and haemoerythrin, are also pigments found in various animals, but they are not involved in transporting oxygen in mammalian blood. Chlorocruorin is found in some marine worms and transports oxygen in their blood, melanin is a pigment responsible for skin coloration, and haemocyanin and haemoerythrin are pigments found in the blood of some invertebrates that transport oxygen.
Question 21 Report
Pests can be controlled without the subsequent danger of polluting the ecosystem by
Answer Details
Pests can be controlled without the subsequent danger of polluting the ecosystem by increasing the population of the natural enemies of the pest. Natural enemies of pests can be other organisms such as predators, parasites, or pathogens, that can help to control the pest population naturally. By increasing the population of these natural enemies, pests can be controlled without using harmful chemicals that can pollute the environment. This method of pest control is known as biological control or biocontrol, and it involves the release of natural enemies or the creation of conditions that encourage their natural presence in the ecosystem. Biocontrol is an effective and sustainable method of pest control that can help to reduce the use of pesticides and promote a healthy ecosystem.
Question 22 Report
The light - sensitive layer is labelled