Haploid:- When only one set of chromosomes are present in the nuclei. (one of each chromosomes.)
Diploid:- Two complete sets of chromosomes are present in the nuclei. (two of each chromosomes.)
Homolougus Pairs:- Chromosomes that are similar in structure and carry the genes (not allways the same alleoles) in the same position.
Chromosomes:- Tightly coiled packages of DNA
Chromosomes replicate into chromatids attatched at a centromere durin interphase.
Interphase is 95% of the cell division process.
G1- The cell, its contents and organelles are copied.
S- The 46 chromosomes are duplicated by the cell into chromatids. This is DNA synthesis.
G2- The cells are then 'double checked' A mutation could have harmful consequences on the cell.
Mitosis begins- Chromatin condenses and becomes inactive. Centrioles migrate in pair poles. Spindles begin to form and centrioles move. The nuclear envelope and nucleolus break down. The chromatids coil up and are now tight .
Mitotic spindle grows further and attaches to the centromere of each chromatid. Fibres then change the chromatid to line up along the cell equator.
The centromere of each chromotids separate into daughter chromosomes. The cell begins to elongate as cytokinesis begins.
New nuclear membranes and nucleoli form. The chromatids begin to wind back into chromosomes and are no longer visible under the microscope.
Finally the cytoplasm divides into two new daughter cells to finish the cycle. Each new cell enters interphase and resumes its normal function.
Where is Mitosis found found in nature?
- Growth in normal animals.
- Asexual reproduction in plants.
- Budding in yeast- single cell organisms reproduce this way.
- Cell division takes place in a developing embryo.
- Repair of cell damage.
- Replacement of worn out cells.
- Growth in shoot tips and root tips in plants.
Budding Cycle in Yeast
Meiosis and Mitosis
Meiosis:- Genetically non identical cells produced, Produces haploid cells, Only occurs in reproductive cells, Produces 4 daughter cells.
Mitosis:- Genetically Identical cells produced, Produces diploid cells, Occurs in growth and repair, Produces 2 daughter cells.
- Unspecialised, can repeatedly divide, can differentiate.
- Totipotent:- stem cells that have the ability to become ANY cell type (e.g. early embryo)
- Pluripotent:- Stem cells that have the ability to become ALMOST any cell type.
- Multipotent:- Stem cells that have the ability to become only ONE OF A FEW cell types. (e.g. in bone marrow cells can either become red or white blood cells.)
- Differentiation:- The specialisation of a cell to carry out a particular function.
Mitosis in Plants
In a region of a plant called the cambien there are cells named the meristematic cells which are partially specialised. They're found in the root tips and shoot tips of plants. They're what makes the xylem and the phloem.
Specialised cells- Neutrophils
(white blood cells e.g. phagocytes) Defend body against disease. Adaptations:-
- Flexible shape to engulf foreign particles and pathogens.
- Many Lysosomes in the cytoplasm containing digestive enzymes to break down and engulf particles.
- A multi lobed nucleus.
- Strong Cytoskeleton for movement.
- Ribosome's, rough ER and golgi for protein-synthesis to make enzymes.
- Mitochondria for energy for movement.
- Receptors on the surface to find anti-bodies.
(Red blood cells) Carry Oxygen in the blood. Adaptations:-
- Biconcave disc shape provides large surface area for gas exchange.
- No nucleus so more room for haemoglobin.
- Protein to carry Oxygen.
- Very small so can easily flow and travel through capillaries and get very close to body cell tissue
Adaptations of cell:-
- Cover organs surface, with cilia on edges.
- Joined by interlinking cell membranes at there base.
- Some have cilia on edges which beat to move particles away.
- Some have micro-villi folds in the cell to increase the cells surface area for an increased absorption rate into the cell.
(Male sex cell) Adaptations:-
- Have flagellum (tail), so they can swim to the egg.
- Acrosome contains digestive enzyme to enable the sperm to penetrate the surface of egg.
- Contains a haploid number of cells so when it joins with the egg the number becomes diploid.
- Microtubles move over each other to move the flagellum for cell movement.
- Mesophyll cells in leaves do majority of photosynthesis so contain most chlorophyll and chloroplasts.
- Thin cell wall so CO2 can diffuse through into the cell.
Root Hair Cell
- Absorb water and mineral ions in the soil.
- Large surface area for absorption.
- Thin, permeable cell wall for entry of ions and water.
- Extra mitochondria to provided energy needed for active transport.
- Line stomata- tiny pores in surface of the leaf used for gas exchange.
- When it's light, the guard cell becomes turgid- then the thin outer walls and the thick inner walls force them to bend outwards opening the pore.
- This allows gases to exchange via photosynthesis.