B5 Growth and Development Revision Powerpoint

Cell Division Why do cells divide? Growth Reproduction Replace damaged cells

Mitosis – making new body cells Put the stages of mitosis in the correct order Chromosomes separate and move to opposite ends of the cell The cell grows and copies organelles The cell has 2 copies of each chromosome and lots of mitochondria The cell divides to make 2 identical cells Answer: 2 3 1 4

Meiosis – making sex cells gametes Arrange the stages in order: The original cell splits into 2 The 2 cells split into 4 daughter cells The chromosomes copy The chromosomes separate The chromosomes separate again Answer: 3 4 1 5 2

Compare mitosis and meiosis in human cells Features Mitosis Meiosis No. of chromosomes in mother cell 46 No. of daughter cells 2 4 No. of chromosomes in daughter cells 23 Used in Asexual reproduction, growth and repair of cells Making gametes

Fertilisation Egg + sperm zygote 23 + 23 46 chromosomes

DNA and the Genetic Code DNA is the molecule chromosomes are made of The genetic code is the info needed to make a body The genetic code is stored in your chromosomes Each chromosome has many genes on it

The Double Helix A DNA molecule is 2 strands twisted together. The bases always pair in the same way – this is base pairing Adenine joins with Thymine Guanine joins with Cytosine

Copying DNA Arrange in the correct order The 2 strands separate The cell contains free bases which start to make new strands The 2 new stands are identical to the original strands Bonds between the bases split G and C pair, A and T pair Answer: 4 1 2 5 3

Making Proteins Proteins are made of a______ a_____ joined together. Three bases code for 1 amino acid – this is the t_______ c_______ The gene on the DNA is copied by making m_____. mRNA leaves the nucleus and goes to the r_________

How is DNA and mRNA different? Single stranded Double helix Bases are A, U, G, C Bases are A, T, G, C

Embryo Development Up to the 8 cell embryo all cells are unspecialized embryonic stem cells All the genes are switched on

Gene Switching Every nucleus contains all the genes Some genes are switched off because they are not active Eg amylase is only made in salivary cells and keratin is only made in hair cells

Stem Cell Technology (HT) Scientists hope to treat diseases and replace damaged tissues with stem cells Stem cells come from umbilical cord blood, early embryos and adults Some people have ethical objections to using them Tissues grown from embryonic stem cells have different gene to the person receiving the transplant and patients need drugs to stop rejection Adult stem cells have most of their genes switched off and can only grow into a few cell types

Therapeutic Cloning Arrange the sentences! The stem cells can develop into different organs and tissues. The egg cell makes an embryo. Its genes are the same as the patients genes Transplant the organ or tissue into a patient. Take a nucleus out of a human egg cell. Replace it with a nucleus from a body cell of the patient. After 5 days put the stem cells from the embryo in a dish of nutrients Answers: 4 2 5 1 3

Growth and development in plants Specialised cells are found in organs such as l_______, r______, s________ and f_________. Some cells remain unspecialised – these are the m_________ cells found in the root and s______ tips and in rings around the stems and roots.

Phototropism – growth towards light The hormone is called auxin

Cuttings Plant cuttings are clones of the parent plant. Rooting powder contains auxin to encourage cell growth.