In higher animals, most cells with the exception of the nerve cells retain their power of division. Thus, there is a continued breakdown and replacement of cells. Animal cells undergo rapid cell division and cell differentiation but, unlike plant cells, they undergo very little cell enlargement. In most animals growth occurs throughout their life till…
PLANT GROWTH & HORMONES What is plant hornmones? Plant hormones are chemicals produced in very small amounts within the plant body, and play a very important part in regulating plant growth and development. Most growth hormones are produced at the tip of a shoot and transported downwards to the root. The root tip produces very…
PRIMARY AND SECONDARY GROWTH The region of growth in plants is found in localized areas called meristems. A meristem is a group of undifferentiated cells in plants which are capable of continuous mitotic cell division. The main meristems in flowering plants are found at the tips of shoots and roots, in young leaves, at the bases…
SEED GERMINATION: DEFINITION, TYPES, FACTORS & PROCESS What are the types of germination? The nature of germination varies in different seeds. During germination the cotyledons may be brought above the soil surface. This type of germination is called epigeal germination. If during germination the cotyledons remain underground the type of germination is known as hypogeal….
SEED GERMINATION CONDITIONS, CONDITIONS NECESSARY FOR GERMINATION What are the conditions necessary for seed germination? Seeds can easily be destroyed by unfavourable conditions such as excessive heat, cold or animals. Seeds need certain conditions to germinate and grow. Some of these conditions are external, for example water, oxygen and suitable temperature while others are internal…
SEED STRUCTURE What is the seed structure? A typical seed structure consists of a seed coat enclosing an embryo. The seed coat is the outer covering which, in most seeds, is made up of the two layers, an outer testa and inner one, the legmen. The testa is thick; the tegmen is a transparent membrane…
Requirements Small plots/boxes, meter rule and seeds of beans (or green grams, peas, maize), Procedure Place some soil in the box or prepare a small plot outside the laboratory. Plant some seeds in the box and place it in a suitable place outside the laboratory (or plant the seeds in your plot). Water the…
GROWTH AND DEVELOPMENT Concept of Growth and Development Growth is a characteristic feature of all living organisms. Most multicellular organisms start life as a single cell and gradually grow into complex organisms with many cells. This involves multiplication of cells through the process of cell division. This quantitative permanent increase in size of an organism…
BIOLOGY PRACTICAL ACTIVITIES 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…
SECONDARY SEXUAL CHARACTERISTICS What are secondary sexual characteristics? 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…
GESTATION PERIOD 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….
FERTILIZATION IN ANIMALS 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…
REPRODUCTION IN HUMANS: Ovaries, Uterus, Cervix, Vagina, Testis, Prostate gland, etc. The female reproduction 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…
REPRODUCTION IN ANIMALS 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…
Animal dispersal Fleshy fruits are eaten by animals. Animals are attracted to the fruits by the bright colour, scent or the fact that it is edible. The seeds pass through the digestive tract undamaged and are passed out with faeces. E.g. tomatoes and guavas. Such seeds have hard, resistant seed coats. Others have fruits with…
PLACENTATION 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…
POLLINATION 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…
SEXUAL REPRODUCTION IN PLANTS 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…
REPRODUCTION IN PLANTS AND ANIMALS Introduction 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 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….