B2

Mitosis:

Used for normal cell growth

• Parent cell
• Chromosomes make identical copies of themselves
• They line up along the centre
• They move apart
• Two daughter cells from each with 46 identical chromosomes to the parent cell.

Meiosis:

Used to make the sex cells (gametes)

• the chromosomes are copied
• Cells divide twice to give four cells

Sexual:

Variation is introduced by:

• Set of genetic info from two parents
• The gametes are produced by meiosis (each gamete is different)
• Some inherited characteristics may be more dominant than others e.g: eye colour, brown and blue.

Asexual: example: a spider plant.

• One parent
• Offspring produced by mitosis
• Genetically identical to the parent
• Are a clone of the parent
• There is NO variation!

Genetics:

Nucleus->Chromosome->Gene->DNA double helix->Bases

46 Chromosomes to fertilised egg, 23 from each parent.

• Male= x,y the male determines the sex of the baby
• Female= x,x

If there is an extra chromosome= downs-syndrome.

DNA is a double helix

The order of bases A, T, C, G determine our features

• A=Adenine   A always pairs with T      A sequence of 3 bases codes for
• T=Thymine                                         one amino acid. The sequence of
• C=Cytosine  C always pairs with G     amino acids determine the protein
• G=Guanine                                         structure and characteristics.

Constant internal environment.

Temperature in the Thermoregulation system

Too hot:

• hair lies flat
• blood vessels dilate-sweat
• flush-capillaries close to skin

Too cold:

• goosebumps-hair traps air
• no sweat
• shivering-generates heat
• blood vessels constrict. 

Cell Organelles

Both Animal and Plant cells:

• nucleus-controls cell functions (brain)
• cell membrane-controls entry of chemicals into cell
• cytoplasm-where chemical reactions happen
• mitochondria-respiration
• endoplasmic reticulum-makes proteins like enzymes

Plant ONLY:

• cell wall-supports cell (protection)
• chloroplasts-site of photosynthesis (chlorophyll)
• vacuole-contains sap and starch granules