Examining the stages of mitosis About 2 mm of a root tip of onion bulb is cut off and placed on a microscope slide. A stain e.g. aceto-orcein is added and the root tip macerated using a scapel. A cover slip is added and observations made. Different stages of mitosis can be observed. Examining the […]
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Male Sexual Characteristics Testerone is the main androgen that stimulates the development of secondary sexual characteristics. Broadening of the shoulders. Deepening of the voice due to enlargement of larynx. Hair at the pubic area, armpit and chin regions. Penis and testis enlarge and produce sperms. Body becomes more masculine. Female Enlargement of mammary glands. Hair
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What is Gestation Period? The period between conception and birth is called gestation. In humans gestation takes nine months (40 weeks). The embryo differentiates into tissues and organs during this period. Week 1 to 3: Zygote divides to form blastocyst. Implantation takes place. The three germ layers form endoderm, mesoderm and ectoderm. Nervous system starts
What is fertilization in animals? Fertilization is preceded by copulation in which the erect penis is inserted into the vagina. This leads to ejaculation of semen. The sperms swim through the female’s genital tract to the upper part of the oviduct. The head of the sperm penetrates the egg after the acrosome_ releases lytic enzymes
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The female reproductive system consists of the following: Ovaries Are two oval cream coloured structures found in lower abdomen below the kidneys. Oviducts. They produce the ova. Are tubes which conduct the ova produced by the ovaries to the uterus. Fertilization occurs in the upper part of the oviduct. Uterus What is uterus? Uterus is
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What is reproduction in animals? Sexual reproduction involves the fusion of gametes. In animals two individuals are involved, a male and a female. Special organs known as gonads produce gametes. In males testes produce sperms while in females ovaries produce ova. The fusion of male gamete and female gamete to form a zygote is called
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What is placentation? This is the arrangement of the ovules in an ovary. Marginal placentation: The placenta appears as one ridge on the ovary wall e.g. bean. Parietal placentation: The placenta is on the ridges on ovary wall. Ovules are in them e.g. pawpaw. Axile placentation: The placenta is in the centre. Ovary is divided
What is pollination? This is the transfer of pollen grains from the anther to the stigma. Types of pollination Self pollination is the transfer of pollen grains from the anther of one flower to the stigma of the same flower. Cross-pollination is the transfer of pollen grains from the anther of one flower to the
What is sexual reproduction in plants? In flowering plants, the flower is the reproductive organ which is a specialised shoot consisting of a modified stem and leaves. The stem-like part is the pedicel and receptacle, while modified leaves form corolla and calyx. Structure of a flower A typical flower consists of the following parts: Calyx
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The process by which mature individuals produce offspring is called reproduction. Reproduction is a characteristic of all living organisms and prevents extinction of a species. There are two types of reproduction: sexual and asexual reproduction. Sexual reproduction involves the fusion of male and female gametes to form a zygote. Asexual reproduction does not involve gametes.
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What is Asexual reproduction? Asexual reproduction is the formation of offspring from a single parent. The offspring are identical to the parent. Types of asexual reproduction. Binary fission in amoeba. Spore formation in Rhizopus. Budding in yeast. Binary fission This involves the division of the parent organism into two daughter cells. The nucleus first divides
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Ecology is best studied outdoors. Students identify a habitat within or near the school compound, e.g. a flower bed. The quadrat method is used. Observation and recording of the various animals as well as their feeding habits is done. Birds that feed on the plants or arthropods in the area studied are noted through observation
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Ascaris lumbricoides Ascaris lumbricoides lives in the intestines of a man or pig, feeding on the digested food of the host. The body of the worm is tapered at both ends. The female is longer than the male. Mode of transmission The host eats food contaminated with the eggs, the embryo worms hatch out in
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The term disease denotes any condition or disorder that disrupts the steady state of wellbeing of the body. Health is a state of physical, mental and emotional wellbeing in the internal environment of the body. Some of the causes of diseases are due to entry of pathogens and parasites. Pathogens include bacteria, viruses, protozoa and
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What is pollution? This is the introduction of foreign material, poisonous compounds and excess nutrients or energy to the environment in harmful proportions. Any such substance is called a pollutant. Effects of Pollution on Human Beings and other Organisms Effects and Control of causes of Pollutants in Air, Water and Soil Industrialisation and urbanisation are
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What is hydrophytes (water plants)? Water plants are submerged, emergent or floating. Submerged Plants The leaves have an epidermis with very thin walls and a delicate cuticle. They have no stomata. Water is excreted from special glands and pores at the tips. Other adaptations include the following: Presence of large air spaces and canals (aerenchyma)
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What is population estimation methods? It is important to find or estimate the sizes of the different populations in a habitat. Direct counting or head count which involves the counting of every individual is not always applicable for all organisms. e.g., it is impossible to count directly the numbers of grasshoppers in an area. Different
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What is a food chain? A food chain is a linear relationship between producers and consumers. It represents the transfer of food energy from green plants through repeated stages of eating and being eaten. Types of Food Chain Grazing food chain – starts with green plants. Detritus food chain – starts with dead organic material
The relationships between organisms in a given ecosystem is primarily a feeding one. Organisms in a particular habitat have different feeding levels referred to as trophic levels. There are two main trophic levels: Producers: These organisms that occupy the first trophic level. They manufacture their own food hence are autotrophic. Consumers: These are the organisms
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What is Ecosystem? The community and the abiotic or non-living environment together make up an ecosystem or ecological system. In this system energy flow is clearly defined from producers to consumers and nutrient cycling takes place in paths that links all the organisms and the non-living environment. Biomass This is the mass of all the