Category: A-level Biology
Explain why measles vaccine administered at the age of 9 month
It was estimated that weaning on average occurs at this age, and the baby no longer gets antibodies against measles from the mothers. Read More
Explain why the impermeability of an axon membrane to sodium ion in part of a neuron helps to maintain resting potential in that part of the neuron
Impermeability of the membrane prevents entry of sodium ions which would cause depolarization Read More
Explain why sickle cell trait is prevalent in malaria prone areas
Sickle cell trait is caused by a recessive allele in heterozygote state. Malaria acts as a selection pressure for heterozygote promoting their high occurrence in ... Read More
When light and temperature are optimum while carbon dioxide concentration is low, the rate of photosynthesis can’t increase further.
In isolated populations mutations and natural selection occurs differentially leading to evolution of new species Read More
In the universe we live on planet earth, • is the third planet from the Sun at a distance of about 93 million miles (150 million km). • is spherical with a radius of about 6,400 kilometers; • is the biggest of the terrestrial planets and the fifth largest planet overall • has a total surface Area of about 510 000 000 square km; 21% of which is land and 71%of which is covered by water. • Has a mass of 60,000 billion tones • The sun is the main source of energy (light and heat) • has average temperature of 150C Earth structure – The structure of the earth is divided into four major components: the crust, the mantle, the outer core, and the inner core. – Each layer has a unique chemical composition, physical state, and can impact life on Earth’s surface. – Movement in the mantle caused by variations in heat from the core, cause the plates to shift, which can cause earthquakes and volcanic eruptions. – These natural hazards then change our landscape, and in some cases, threaten lives and property. Spinning and Rotation of the earth – The earth spins on its axis once in 24 hours producing night and day, – The Earth revolves in orbit around the sun in 365 days, 6 hours, 9 minutes leading to changes in seasons. Plate tectonics – Plate tectonics is a scientific theory that explains how major landforms and water bodies are created as a result of Earth’s subterranean movements. – Plate tectonics is the theory suggests that that the Earth’s outer shell/crust is divided into several rigid plates/sections called tectonic plates. These float and glide over the mantle leading to changes in the earth’s surface – There are seven major plates: African, Antarctic, Eurasian, Indo-Australian, North American, Pacific and South American. Theories of continental drift – Continental drift is the hypothesis that the Earth’s continents have moved over geologic time relative to each other and are still moving even today. Several theories of continental drift have been advanced including F.B Tailor’s theory of continental drift – Accord¬ing to Tailor, originally, there were two land masses Lauratia and Gondwanaland lo¬cated near the north and south poles respectively. – These moved closer towards the equator because the moon came closer to the earth and exerted powerful tidal and gravitational forces on them. – Lauratia started moving away from the North Pole because of enormous tidal force of the moon towards the equator in a radial manner. This movement of land mass resulted into tensional force near the North Pole which caused stretching, splitting and rupture in the landmass. Consequently, Baffin Bay, Labrador Sea and Davis Strait were formed. – Similarly, the dis¬placement of the Gondwanaland from the South Pole towards the equator caused splitting and disruption and hence the Gondwanaland was split into several parts. Consequently, Great Australian Bight and Ross Sea were formed around Antarctic Continent. – Arctic sea was formed between Greenland and Siberia due to equator ward movement of Lauratia. Atlantic and In¬dian oceans were supposed to have been formed because of filling of gaps between the drifting continents with water. Taylor assumed that the landmasses began to move in lobe form while drifting through the zones of lesser resistance. Thus, mountains and island arcs were formed in the frontal part of the moving lobes. – The Himalayas, Caucasus and Alps are considered to have been formed during equator ward movement of the Lauratia and Gondwanaland from the north and south poles respectively while the Rockies and Andes were formed due to westward movement of the land- masses. Criticism of F.B Tailor’s theory of continental drift – Tailor failed to explain why the moon came close to the earth at that time. – It doubtable if the moon could exert that strong force to pull the two super continents together. If at all the moon came closer and exerted such a strong force, the earth’s rotation would have stopped within one year but this was not evidence. – According to Tailor, mountain building was through tidal attraction. He failed to explain the origin of mountains e.g. Caledonian which existed before tidal attraction Theory of sea flow spreading – It was advance by an American geologist named Henry Hess who based his theory after studying the bed of the Atlantic Ocean in which he observed presence of ridges between Africa and America. – Seafloor spreading occurs when the sea floor move apart along both sides of a mid-ocean ridge as new crust is added by volcanic activity. As a result, ocean floors move like a conveyor belt, carrying continents along with them. The Evidence in support of seafloor spreading – Pillow-shaped rocks found on the ocean floor could only have formed when molten material hardened quickly after erupting underwater. Instead, these rocks showed that molten material continuously erupts along the mid-ocean ridge – The magnetic polarity of the seafloor changes. The center of the ridge is of normal polarity. Stripes of normal and reverse polarity are found symmetrical on both sides of the ridge. – The youngest seafloor is at the ridge. The oldest is farthest from the ridge. This indicates that new rocks a are continuously forming at the ridges Alfred Wegner’s theory of continental drift Assumptions – Wegner’s theory is based on the rifting and drifting of continents. – Wegner’s theory assumed that there was one giant Sialic landmass (super continent) known as Pangaea, which was located in the south near the present day South Pole, surrounded by a huge expanse of water (Ocean) known as Panthalassa – During the Precambrian period (Permian times about 250million years) Pangaea begun rifting and drifting northwards. – Pangaea cracked and broke into land masses i.e. Laurasia and Gondwanaland were separated by a narrow sea of Tethys (universal sea). – At about l35million years ago, Gondwanaland and Laurasia drifted north wards leading to the closure of the Tethys Sea in the East – Laurasia split into North America, Eurasia and Green land, Iceland while Gondwanaland split into Africa, South America, India, Austria and Antarctica. – During the drifting the Oceans between the continental blocks became wider, forming the present day ocean basins like Atlantic, pacific etc. – In the North, Eurasia drifted East wards. – In the South, Africa moved to attain its present locations astride the equator. – South America drifted westwards and Northern wards to join north America – India drifted northwards to join Eurasia. Australia drifted Eastwards, away from Antarctica about 65million years ago. Relevancy/Evidences to support Wegner’s theory – Jigsaw/Visual fit of continents. There is a close fitting (Jigsaw puzzle) of the continental coastlines across the Atlantic ocean i.e. the East coast of South America and West coast of Africa have good visual fit (ach fit into one another) not only at the surface but also at 2000m deep. – Geometric fit of continents. The west coastline of Africa and the Eastern coastline of South America fit almost exactly on each other if rotated at an angle of 570 with rotational point 400N and 300 E – Matching geological/similarity in rocks and rocks bearing minerals which appear continuous. E.g. Africa and South America have rocks with a convincing boundary joined between Accra and Saolouis in Brazil, the coal bearing rocks of Eurasia and North America (the Appalachiana). The gold bearing rocks of West Africa (Ghana) and South America (Guyana). – Similar oil beds. Oil beds in Brazil are similar to those of Angola in Africa. – Matching orogenic zones/belts. The alignment of the belts of fold mountains matches across the joint of Africa and America e.g. folded ranges in Falkland Islands and Argentina are similar in age and structure to those of the south west cape of South Africa-the cape ranges. – Glacial evidence (Dwyka Tillite) thick deposits of tillite (fossilized glacial moraine) in Eastern Brazil, Paraguay and Argentina, are exactly like those of South Africa and Australia implying that the continents at one time were near or too close to each other. – Similar sedimentary Basins. A long part of North Eastern Brazil coast, South Nigeria and Cameroon, similar sedimentary rocks sequences exist and the low beds of that basin match exactly on both continents. – Similarity in plant and animal species in Australia and south Africa; Africa And south America – Palaeomagnetic evidence; Palaeomagnetism refers to ancient or foddil magnetism in rocks. It’s based on the fact that igneous rocks when cooled retain some magnetic properties which at time of magnetization point the earth’s north-south. However, studies indicated that India, Australia, South America, the magnetic properties in the magnetized rocks no longer point in the north-south direction as it should be suggesting that during the course of drifting, rocks were twisted and changed direction. – Existence of laterites in North America and Europe proves that these continents experienced tropical climatic conditions for formation of laterites. But with time drifted to the temperate region. – Existence of coral reefs in the Green land, Britain, North America and yet coral reefs form in hot climatic conditions. – Salt evaporites/beds in cold parts of U.S.A, Britain, Germany and Russia is evidence for continental drift from tropics because salt evaporites occur in tropics – Proximity of continental land masses to the North Pole than in South Pole. – Existence of Fold Mountains justifies the theory of continental drift. Fold mountains form when there are compressional forces acting in the same direction e.g. Mt. Himalaya – Identical fossils on different continents for example the ancient reptile mesosaurus are only found in southern Africa and South America yet it is not evident that it swam across Atlantic ocean The theory of plate-tectonics – It is the most modern theory of continental drift – It explains the movement and distribution of present day continents, ocean basins and land forms – It proposes that the earth crust is divided into individual separate parts/tectonic plates by geochemical reactions and radioactivity in the earth’s interior. These float and move/glide on the top of Earth’s interior mantle. – The movements of the tectonic plates results in the movement of continents /land masses and water bodies and change their positions relative to each other. – Generally all plates move northwards, others like America move westwards while Africa, Europe, Asia, Australia move north eastwards. – There are 3 types of plate movements/boundaries caused by convection currents which influence the distribution of continents i.e. (i) Divergent movements; caused by tectonic plates moving away from one another. These lead to faulting, rifting and warping of crustal land masses. On the sea floor, divergent movements produce under-water mountains known as the mid-ocean ridge for example the mid-Atlantic ridge and islands (ii) Convergent movement; caused by tectonic plates moving towards one another. And as a result;¬ continental land masses may move towards each other getting closer, collision may occur leading to folding and formation of fold mountains e.g. the Himalayas due to the collision of India and Asia. (iii) Continents may move towards Oceanic plates causing subduction of denser simatic rocks. Collision of plates and subduction leads to formation of trenches, volcanic and fold mountains e.g. Nazca , Java and Tonga trenches etc. – Oceanic crust may move towards each other causing narrowing of Ocean Basins and continents move nearer leading to formation of trenches and volcanic arcs e.g. Pacific and Eurasia plates moved towards each other Marina trench and Japan volcanic arc were formed. – Plate tectonism is responsible for land forms due to vulcanicity, faulting and warping Definitions Tectonic plates Tectonic plates are blocks of continental and ocean crust. The earth’s surface is divided into blocks of continental and oceanic crust Characteristics of tectonic plates – Plates are relatively light and therefore float on the denser rocks of the mantle and asthenosphere. – Plates are mobile and move extremely slow on rocks of the upper mantle and driven by convective currents generated by radioactivity and geochemical reactions in the core and the mantle. – A given plate is so rigid that if one part move, the rest move Continental crust (SIAL) Continental Crust Continental crust is made up of very old light rocks (average density 2.6) of different granites. SISAL stands for silicate and aluminum, the most abundant minerals in continental crust Oceanic Crust (SIMA) Oceanic crust is made up of heavy basalt rocks (average density 3) and thickness between 5-10 kilometers (3-6 kilometers). SIMA stands for silicate and magnesium, the most abundant minerals in oceanic crust Types of plate tectonic boundaries – A divergent boundary (constructive plate boundary/margin) occurs when two tectonic plates move away from each other widening the gap between the plates. Along these boundaries, earthquakes are common and magma (molten rock) rises from the Earth’s mantle to the surface, solidifying to create new oceanic crust. Examples include divergent tectonic boundaries include The Mid-Atlantic Ridge. – A convergent boundary occurs when two plates come together narrowing the gap between the plates. The impact of the colliding plates can cause the edges of one or both plates to buckle up into a mountain ranges or one of the plates may bend down into a deep seafloor trench. A chain of volcanoes often forms parallel to convergent plate boundaries and powerful earthquakes are common along these boundaries. The Pacific Ring of Fire is an example of a convergent plate boundary. At convergent plate boundaries, oceanic crust is often forced down into the mantle where it begins to melt. Magma rises into and through the other plate, solidifying into granite, the rock that makes up the continents. Thus, at convergent boundaries, continental crust is created and oceanic crust is destroyed. – A transform plate boundary (transform plate margin) occurs when two plates sliding parallel past each other. One of the most famous transform plate boundaries occurs at the San Andreas fault zone, which extends underwater. Natural or human-made structures that cross a transform boundary are offset — split into pieces and carried in opposite directions. Rocks that line the boundary are pulverized as the plates grind along, creating a linear fault valley or undersea canyon. Earthquakes are common along these faults. In contrast to convergent and divergent boundaries, crust is cracked and broken at transform margins, but is not created or destroyed. Lateral and vertical Earth movement Lateral earth movements – They are diastrophic/large scale differential movements that operate horizontally within the earth crust. – They are caused by internal forces i.e. tensional forces (divergent forces) and compressional forces (convergent forces}, with resulting strains and stresses in the rocks. – They lead to folding and faulting of the coast While Vertical earth movements – They are diastrophic movements that operate vertically exerting a pushing force onto the crust either upward or downward along a radius from the centre of the earth to the surface. – They usually occur on a large scale hence called epeirogenic (slow large scale uplift) and may involve vertical uplift or subsidence. – Possibly the result of isostatic readjustment, or warping and titling may be on a local scale especially around the coast, thus affecting the relative level of land and sea and therefore the nature of the coastline. Also lead to warping and tilting. Earthquake An earthquake is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth’s lithosphere that creates seismic waves/vibration/tremors. Most earthquakes occur within the crust of the earth and not at the surface. The point from which the shock waves originate is known as the focus and the point directly above on the surface is known as the epicenter. The shock waves pass very rapidly through the rocks to the surface where the shaking can cause destruction of life and property. The Richter magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs. Causes earthquakes Earthquakes are caused due to sudden tectonic movements in the earth’s crust. When the tectonic plates slide over one another, or collide there is a cause of orogeny which results in earthquakes and volcanoes. These disturbances cause vibrations that spread in all directions The energy that drives earthquake is generated by radioactivity and geochemical reactions tgat give to the development of convective currents. Body waves are seismic waves generated during earthquakes and travel through the earth’s interior, spreading from the focus in all direction. They can be p-waves/longitudinal waves or s-waves of transverse waves. Surface waves are seismic waves that travel on the surface away from epicenter. They are classified as Love waves (transverse waves)or Rayleigh waves(longitudinal waves) both of which are destructive to property and lives. Effect of earthquake – Destruction of lives and property – Advancement of technology to construction of earthquake resistant properties – Triggered technology for understanding different land forms – Employment such as in education Revision questions 1. Discuss any four theories which have been put forward to ascertain the occurrence of continental drift. 2. (a) what is meant by the term plate tectonic? (b) How does the theory of plate tectonic explain the present day distribution of continents 3. Examine the evidences outlined to justify occurrence of continental drift. 4. Explain the relevance of Wegner’s theory of continental drift to understanding of the present day distribution of continents and oceans. 5. (a) Distinguish between lateral and vertical earth movements. (b) explain the relevance of plate tectonic theory in understanding the present day distribution of ocean and land masses.
When light and temperature are optimum while carbon dioxide concentration is low, the rate of photosynthesis can’t increase further. Read More
Explain the effects of the heterozygote advantage in a population with increasing gene
Increasing gene flow reduces the probability of recessive alleles or disadvantageous alleles in the population as it introduces new alleles. This reduced the selection pressure ... Read More
State four physiological differences between C3 and C4 plants.
Difference between C3, and C4 plant C3 pathway C4 pathway 1 Photosynthesis occurs in mesophyll cells Photosynthesis occurs in mesophyll cells and bundle sheath cells ... Read More
Explain how light influences stomatal opening in a plant that has been previously in the dark.
When exposed to light, starch of the guard cells is converted into malic acid, Malic acid dissociate into malate and H+ ions in the guard ... Read More
Does milk contain iron?
Dairy products such as cheese, cottage cheese, milk and yogurt, although rich in calcium, have negligible iron content Read More
What part is played by the mammalian skin in excretion?
Sweating eliminates urea, a by-product of protein catabolism, excess water and salts Read More
What is the role of stored proteins during seed germination
Provide a source of amino acids and reduced N necessary for synthesis of enzymes, and for formation of structures in developing embryo. some may be ... Read More
Methods to reduce soils erosion are
Afforestation Planting grass cover Mulching Strip cropping Terracing Contour cropping Read More
Types of soil erosion
Sheet erosion: the surface of the soil is removed evenly over the whole surface of a slope Rill erosion: top soil is removed to an ... Read More
What is soil erosion?
It is the washing away to soil Read More
Effects of adrenaline in the body.
increase rate of heart beat increases rate of breathing increases metabolic rate increase blood pressure and increases blood flow to brain and muscle enlarges pupil ... Read More
What’s the difference between endocrine and exocrine glands?
Exocrine glands secrete their substances through ducts onto your body's surfaces. On the other hand, endocrine glands secrete their substances directly into your bloodstream Read More
What are the differences in blood contents between the blood carried by hepatic portal vein and hepatic vein?
Blood in the hepatic portal vein is rich in nutrients from the intestine Read More
Name the constituents of the mammalian blood
plasma, red blood cells, white blood cells, and platelets, water, food nutrients (glucose, amino acids, fatty acids, vitamins), waste products (like urea and ammonia) hormones, ... Read More
How does clay affect the fertility of soil?
Contain plant nutrients Increases soil capillarity Increase soil water retention Provide firm anchorage to the plants Read More
Explain the value/importance of earthworms in maintaining a condition suitable for crop growing.
. Tunnels improve aeration and drainage of soil causes decay and formation of humus source of food to other animals e.g. chicken die and rot ... Read More
Describe an experiment to demonstrate hydrotropism in plant roots and shoots.
Hydrotropism: 1. Hydrotropic movements refer to a plant's movement or growth in response to a water stimulus, while hydrotropism refers to the analogous response to ... Read More
Benefits of studying genetics
helps researchers develop new strategies to treat and prevent human disease. Help to understand more about the genetic basis of human diseases. Genetic engineering such ... Read More
Distinguish between dominant and recessive genes
A dominant gene is the one that expresses itself entirely in heterozygous state while a recessive gene is one masked in heterozygous state Read More
Distinguish between phenotype and genotype
Phenotype is the physical characteristic of an organism determined by the genotype and the environment. Genotype is the genetic constitution of an organism i.e. the ... Read More
Adaptations of fish for locomotion/swimming
Streamline shape reduces friction Eye to see in water Pectoral, pelvic and ventral fins for balancing. Slippery body reduce friction Has gills to extract oxygen ... Read More
What is a multiple allele?
The presence of three or more alleles for a given gene is referred to as multiple alleles. Read More
What are sex-linked genes?
Sex linked genes are those that sit on sex chromosomes and that are inherited differently in males and females Read More
What is codominance
Codominance, in genetics, phenomenon in which two alleles (different versions of the same gene) are expressed to an equal degree within an organism. Read More
What does heterozygote mean?
Heterozygous refers to having different alleles for a particular trait Read More
What happens when onion epidermis is placed in strong sugar solution
The cells of the epidermis placed in strong sugar solution lost water by osmosis, and became flaccid Read More
What happens when onion epidermis is placed in water
The cells of the epidermis placed in pure water gained water by osmosis, swell and became turgid Read More
When mucus fills the Eustachian tube, hearing is impaired. Explain why.
It may causes increase in pressure in the middle air which distorts vibration of the eardrum and ossicles Read More
How does the blockade of Eustachian tube affect hearing?
Obstruction or blockage of the Eustachian tube results in a negative middle ear pressure, which will cause the ear drum to retract (suck in). In ... Read More
What is the function of hair and wax in ear canal
Wax and protects the ear from invasion of organisms and keeps away dirt and debris from the ear drum Read More
Adaptations of insect pollinated flowers and wind pollinated flowers
Note that there is a difference between characteristics and adaptations of flowers Adaptations of Insects pollinated flowers brightly colored petals to attract pollinators scented to ... Read More
The importance of a skeleton to an organism
Hydrostatic skeleton provides support form movement Exoskeleton1.It minimize water loss by evaporation 2.It protects the internal soft tissue 3.It determine maximum size of the organism ... Read More
Types of skeletons
There are three types of skeleton Hydrostatic skeleton Here support is provided by a fluid under pressure and it is found in round worms, earthworm. ... Read More
Parts of motor neuron/nerve
Functions of parts of nerve cell Nerve fibre or axon transmits impulses The myelin sheath protects the axon; it also insulates the axon and speeds ... Read More
Functions of parts of nerve cell
Nerve fibre or axon transmits impulses The myelin sheath protects the axon; it also insulates the axon and speeds up transmission of impulse. Nucleus controls ... Read More
What happens to old red blood cells in the body?
Old or damaged RBCs are removed from the circulation by macrophages in the spleen and liver, and the hemoglobin they contain is broken down into heme ... Read More
What substances are secreted from sweat glands?
urea, water, sodium chloride, lactate Read More
A-level math paper 1 Inequalities
Please double click and download the PDF below A-level math paper 1 Inequalities Read More
Adaptations of a bony fish to movement in water
- has streamline shape to reduce drag force - has tail fin for propulsion - has fins for stability - has slippery body to reduce ... Read More
Differences between bones and cartilages
Differences between bones and cartilages Bones Cartilages 1 Bone is tough and hard Cartilage is soft and flexible 2 Bones cannot bend Cartilages ... Read More
Pentadactyl limb
It is so called because typically has five digits, is found in all four classes of terrestrial vertebrate some of the limbs bone can even ... Read More
The largest section of the human brain is the …
Cerebrum. The cerebrum (front of brain) comprises gray matter (the cerebral cortex) and white matter at its center. The largest part of the brain, the ... Read More
Describe how the various parts of the human digestive system are adapted to their functions
Adaptations of the mouth for digestion Contains space to receive food by ingestion, contains teeth to break food into small particles by mastication contains saliva to ... Read More
Describe the process of fertilization in human beings.
Fertilization occurs when a sperm fuses with Ovum; during intercourse sperms are released from the testis through the urethra into the vagina. The sperm travels through ... Read More
Adaptations of schistosoma mansoni to the parasitic mode of life
has cilia or tails for swimming to find the host has secretory glands for host penetration, has a tegument and glycocalyx for parasite protection/host immuno-modulation, has ... Read More
What is chistosoma mansoni?
Schistosoma mansoni is a water-borne parasite of humans transmitted by water snail, and belongs to the group of blood flukes. The adult lives in the ... Read More
What is parasitism?
Parasitism is a relationship between two species of plants or animals in which one lives in or on another organism benefits at the expense of ... Read More
To which bones is the biceps muscle attached by tendons?
Finally, the short head of the biceps brachii, due to its attachment to the scapula (or shoulder blade), assists with stabilization of the shoulder joint when a ... Read More
What is thigmotropism?
Thigmotropism is a directional growth movement which occurs as a mechanosensory response to a touch stimulus. Thigmotropism is typically found in twining plants and tendrils, however ... Read More
What is a plant body called that has not differentiated into roots stems and leaves?
Thallophytes are any group of organisms, including algae, fungi, and lichens, that show no differentiation into stem, root, or leaf and were formerly regarded as constituting ... Read More
What is an axial skeleton?
Your axial skeleton is made up of the bones in your head, neck, back and chest. Your appendicular skeleton is made up of everything else — ... Read More
Give the importance to the plants of each of the components that make up a fertile soil.
Soil components and their uses Soil component Use Air Oxygen is particularly required for respiration of micro organism and plant roots; decomposition of organic matter, ... Read More
An experiment to show that germinating seeds liberate carbon dioxide.
Set up Air is drawn over the germinating seeds using a suction pump for some time. Observation Lime water in conical flask D turns milk ... Read More
Testing for presence of starch in leaves
The leaf is boiled in hot water to kill the protoplasm The boiled leaf is placed in boiling alcohol to remove chlorophyll The leaf without ... Read More
Suggest the main functions and deficiency symptoms of nitrogen, magnesium and phosphorus to the plant
ELEMENT FUNCTION EFFECT OF DEFICIENCY Nitrogen Nitrogen is required by plants to produce amino acids, proteins, and DNA. Nitrogen is necessary because it is ... Read More