Cell differentiation Stem cells are unspecialised and they can develop into any type of cell. Totipotency which is when it has the ability to produce all cell types including the specialised cells in an organism and extra-embryonic cells. The second type is...
Variance Continuous variation is when individuals in a population vary within a range with no distinct categories; these can be things like height, mass or skin colour. Discontinuous variation is when individuals are in a specific category, and will fall into only one...
Fertilisation Fertilisation is where male and female gametes fuse. In mammals fertilisation occurs in the oviduct, and in flowering plants it occurs in the embryo sac. Sperm is deposited high up in the vagina, near the cervix. Once there the sperm makes its way up the...
Production of a gametes In animals the male gamete is sperm, and in female it is an egg cell (ova). In plants the male gamete is pollen grains, and the female gametes are ovules. Gametes contain only half the normal amount of chromosomes, so in one gamete in humans it...
The Cell cycle and Mitosis The cell cycle consists of a period of cell growth and DNA replication called interphase and a period of cell division called mitosis. Interphase is sub divided into three separate growth stages These are called G,S and G2. Mitosis is used...
Difference between Prokaryotes and Eukaryotes The organelles found inside a Eukaryotic cell are: There are many differences between Eukaryotes and prokaryotes,:
Protein Transport Transcription occurs when changing DNA to mRNA, where the mRNA leaves the nucleus via pores in the nuclear envelope. Proteins are made on ribosome’s The ribosomes sometimes attach to the rER where the protein made moves through making the 3-D shape...
Cell organisation Genes are expressed through master genes. Such as in fruit flies once the main body segment have been determined, the cells in each segment become specialised for the appropriate structure, (Wings Antennae) The master genes control the development...
THE HUMAN GENOME A genome is all the DNA of an organism or species. In 2001, the Human Genome Project published a working draft of the sequence of bases in human cells. Work continues to identify specific genes and establish their function. Part of the budget for the...
CANCER Cancer occurs when the rate of cell multiplication is faster than the rate of cell death. This causes the growth of a tumour. Cancer is caused by environmental damage to DNA from physical factors such as UV light and asbestos chemical carcinogens such as those...
GENE TRANSCRIPTION The specialised function of a cell depends upon the proteins it synthesises ie which genes are expressed. Transcription of a gene is initiated by RNA polymerase and transcription factors binding to a promoter region (section of DNA adjacent to...
CORE PRACTICAL Sometimes the gene for an enzyme required for the metabolism of a particular substrate can be expressed only when that substrate is present (induction) e.g. and lactose in prokaryotes.
PHENOTYPE Differences in phenotype between members of a population are caused by: genetic make-up (genotype) the environment in which the individual develops Some are due completely to genotype eg blood groups and show discontinuous variation: they fall into...
MITOSIS Mitosis, with identical daughter cells, ensures genetic stability - important for: growth: development from a single cell to a multicellular organism repair: regeneration of lost or damaged parts or replacement of old or damaged cells asexual reproduction eg...
THE CELL CYCLE Mitosis is a type of cell division, which retains the full or diploid number (2n) of chromosomes.In humans, a cell with 46 chromosomes divides to form 2 identical daughter cells, each with 46 chromosomes.Before nuclear division, a copy of each...
GAMETES The sex cells or gametes are adapted for sexual reproduction.
GAMETE PRODUCTION Gametes are produced in the ovaries and testes of animals by meiosis which: produces haploid cells (contain half the number of chromosomes found in a body cell: one of each homologous pair) creates genetic variation among offspring...
DEVELOPMENT OF THE ZYGOTE Fuelled by nutrients from the ovum, the zygote divides rapidly to form smaller cells – the embryo remains the same size. After 3 divisions, there are 8 totipotent stem cells – each could form a total human being. After 5 days, a blastocyst (a...
CELL ORGANELLES (EUKARYOTIC CELL)
PROKARYOTIC CELLS The cells described above, with membrane-bound organelles are eukaryotic.Organisms with eukaryotic cells are classified into 4 kingdoms: Animals, Plants, Fungi and Protoctists.