Unit B5: Growth and Development

Revison of Unit B5: Growth and Development - The genetic code; Cell specialisation; Cell reproduction; DNA

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Unit B5: Growth and Development

REVISION

UNIT B5: GROWTH AND DEVELOPMENT

The genetic code; Cell specialisation; Cell reproduction; DNA

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The genetic code

"Genes are a set of coded instructions for making a particular protein" - Proteins are made outside the nucleus in the cytoplasm

The genetic code consists of four chemical bases: Thymine (T); Anadine (A); Guanine (G); Cytosine (C)
These pair up to make DNA:
Thymine + Anadine
 Guanine and Cytosine 


- Genes code for proteins in triplets

- Each triplet of bases codes for one amino acid

  - Proteins are made up of large numbers of amino acid molecules -

- Amino acids join together to make protein molecules determined by the number and sequence of amino acids


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Cell Specialisation

A zygote is a structure that forms when a sperm fertilises an egg - The zygote then divides many times by mitosis to form an embryo - All cells are identical until the eight-cell stage - these are known as embryonic stem cells
Embryonic stem cells:
It is possible for these stem cells to develop into any specialised cells needed for the embryo. I.e. Nerve cells, Blood cells, Muscle cells. Once these cells become specialised they can not change again.
Cell Specialisation in plants:
- Unspecialised stem cells in plants can develop in to cells of roots, leaves and flowers
- Some plant cells can remain unspecialised, unlike animal cells
- Unspecialised stem cells group together in structures called Meristems - these ensure the plant continues to grow throughout its life
Cloning Plants
Many plants are grown from a cutting of another; this creates an identical copy to the parent cell. The unspecialised cells in the cutting, grow in to tissues such as Xylem and Phloem and organs such as Stem, leaves and flowers
Phototropism
Phototropism is a plant's growth response to light. When the stem grows towards the light, the plant can photosynthesise more. More food is produced, so the plant can grow faster. This increases the plant's chances of survival


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Cell Reproduction

Mitosis - A cell splits to create two identical copies of parent cell - Used when more cells are needed
CELL CYCLE:
- Chromosomes in nucleus are copied
- Chromatids pulled apart and moved towards poles
- Chromosomes separate
- Cell divides
Meiosis - Cells split to form new cells with half No.of chromosomes - Used for male and female gametes
A human body cell contains 46 chromosomes arranged in 23 pairs. Meiosis is sometimes called reduction division.
CELL CYCLE:
- Parent cell
- Chromosomes make identical copies of themselves
- Similar chromosomes pair up
- Sections of DNA get swapped
- Pairs of chromosomes divide
- Chromosomes divide
SPERM = 23 chromosomes    +   
EGG = 23 Chromosomes     =     ZYGOTE = 46 Chromosomes

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