Cells are the building blocks of all living things.
DNA molecules are in the form of a double helix and contain the genetic code
Organelles = different parts of the cell's structure
Animal and plant cells = have cytoplasm, a nucleus, ribosomes and a cell membrane
Plant cells = have a cell wall, permanent vacuole, chloroplasts
Cell Divison and Fertilisation
Mitosis = division of body cells to produce new cells, each new cells contains the same genetic information as the parent cell.
Meiosis = division of cells in the testes and ovaries to produce gametes for sexual reproduction
Gametes = contain half the number of chromosomes as the parent cell.
During fertilisation a male gamete and a female gamete fuse together to produce a zygote.
Zygote = has one whole set of chromosomes
After fertilisation the zygote divides by mitosis to produce an embryo.
Genes = present on the chromosomes in each cell nucleus
- growth and development in organisms
- development of characteristics
Meiosis and sexual reproduction produce variation between offspring and parents as genetic information from two individuals is combined.
Genetic code = made up of 4 bases which hold the two strands of the DNA molecule together
Bases are always paired up in the same way...
- Adenine with Thymine
- Cytosine with Guanine
mRNA = small molecules which leave the nucleus and carry genetic information into the cytoplasm
Ribosomes = follow instructions from the mRNA to make proteins
A group of 3 base pairs codes for one amino acid in a protein chain, called a triplet code. There are 20 different amino acids that can be made.
Embryonic Stem Cells = unspecialised cells that can turn into any kind of cell
After the eight cell stage, the cells in an embryo become specialised and can form different types of tissue.
Stem cells can be used to treat diseases and disorders and repair damage to various tissues.
The three sources of stem cells are embryos, blood from the umbilical cord and adult stem cell.
New cells in plants specialise into the cells of roots, leaves and flowers.
Meristem = area of plant growth, where specialised cells divide repeatedly.
Lateral meristem = leads to increased growth
Apical meristem = leads to increase height and longer roots
Xylem tubes = transports water from roots to stem and leaves and replaces lost water.
Phloem tubes = transports dissolved food to the whole plant for respiration or storage.
Plant Cuttings and Phototropism
New plants develop when cuttings are taken from a plant and put in a rooting hormone.
The new plants are clones of the parent plants.
Auxins = main plant hormones used in horticulture which cause cell growth and division.
Phototropism = growth of plants towards a light source.
Light source overhead - auxin spread evenly - shoot grows straight up
Light source at an angle - ausin on side furthest from light - shoot bends towards light