Cell division, cell diversity and cellular organisation

Question 1

Cell cycle

Answer 1

Cell cycle
- Mitosis, four stages of mitosis: prophase, metaphase, anaphase and telophase
- Cytokinesis, parent and replicated organelles move to opposite sides of the cell and the cytoplasm divides, producing two daughter cells
- Interphase, cell grows and then prepares to divide, chromosomes and some organelles are replicated and chromosomes begin to condense

• During prophase, nuclear envelope breaks down, chromosomes condense, centrioles move to opposite poles for spindle formation
• During metaphase, chromosomes move to equator and attach to spindle fibres via centromeres
• Anaphase, sister chromatids are separated
• Telophase, nuclear envelope reforms, spindle is broken down and chromosomes uncoil

Question 2

Meiosis

Answer 2

Meiosis
- produces haploid gametes
- crossing over of homologous chromosomes occurs in prophase 1 where sister chromosomes condense

Genetic Variation is achieved through:
- Crossing over of chromatids, pairs of chromosomes line up and share some of their genetic materials
- Independent assortment of chromosomes, different combinations of chromosome arrangement

During meiosis 1, homologous chromosomes separate. During meiosis 2, sister chromatids separate
- Prophase 1, resembles the prophase of mitosis but with exception crossing over of homologous chromosomes (at chiasmata)
- Metaphase 1, each pair of bivalents (4 chromosomes) align at the equator. Position of each bivalent is random (random assortment, genetic variation)
- Anaphase 1, Homologous chromosomes separate
- Telophase 1, nuclear envelope reforms
- meiosis 2, another round of cell division occurs, leading to formation of four haploid daughter cells, containing single chromosomes

Question 3

Cellular Organisation

Answer 3

Cellular Organisation
- Xylem, transports water and mineral ions as well provide structural support, made out of dead tissue with open ends, thickened with lignin, produced by meristem cells

• Phloem, involved in the movement of food substances and nutrients from leaves to storage organs and growing parts of the plant, produced by meristem tissue, cells form sieve plates, companion cells are involved in aiding the movement of photosynthesis products upwards and downwards in the tube
• Epithelial, sheet of cells act as a covering. Squamous epithelial cells are smooth, flat and very thin (lining of blood vessels and cheek)
• Ciliated Epithelial cells, column shaped cells containing cilia (trachea, bronchi), The cilia move together to move the mucus produced by goblet cells along
• Connective tissue, provides support and holds various structures together (cartilage and bone)
• Muscle tissue, movement through contraction
• Nervous tissue, impulse conduction

Question 4

Stem Cells

Answer 4

Stem Cells
- Bone marrow blood cells can differentiate into erythrocytes (red blood cells) and neutrophils (white blood cells).