bio - cells and control (2)

• There are 23 pairs of chromosomes in each cell of the body, which you inherit 2 – 46 chromosomes in each cell.
• Gametes contain 23 chromosomes in total in each gamete cell.
• A diploid number of chromosomes is double a haploid number (46 vs 23).
• The cell cycle consists of stages: Interphase, Mitosis, and Cytokinesis.
• Mitosis is the stage when the cell divides.
• In the first stage of the cell cycle, Interphase, the cell grows, organelles (ribosome and mitochondria) grow and multiply, the synthesis of proteins occurs, DNA is replicated, and energy stores are increased.
• During the second stage of the cell cycle, Mitosis, the chromosomes line up at the equator of the cell and cell fibres pull each chromosome of the ‘X’ to either side of the cell.
• The risks include damage to retina or cataracts developing.
• The third stage of the cell cycle, Cytokinesis, results in two identical daughter cells forming when the cytoplasm and cell membranes divide.
• Cell division by mitosis in organisms is important in their growth/development, and replacing damaged cells.
• Mitosis is a vital part of asexual reproduction, as this type of reproduction only involves one organism, so to produce offspring it simply replicates its own cells.
• Mitosis produces 2 daughter cells, each with identical sets of chromosomes to the parent cell (sets of chromosomes in daughter cell’s nucleus = the parent cell’s nucleus – identical diploid daughter cells).
• In animals, growth occurs via cell division and differentiation, with cells differentiating to specialised forms, specially adapted to their function.
• In animals, almost all cells differentiate at an early stage and then lose this ability.
• Most specialised cells can make more of the same cell by undergoing mitosis.
• Others such as red blood cells cannot divide and are replaced by adult stem cells.
• In mature animals, cell division only happens to repair/replace damaged cells – they undergo little growth.
• In plants, growth occurs by cell division and differentiation, but also by a unique process called elongation.
• Plant cells can grow longer in a specific direction by absorbing water into their vacuoles.
• In plants, many types of cells retain the ability to differentiate throughout life.
• They only differentiate when they reach their final position in the plant, but they can still re-differentiate when it is moved to another position.
• Cancer occurs as a result of small changes in cells, that lead to uncontrolled cell division.
• The group of cells that results from this uncontrolled division is called a tumour.
• Percentiles charts can tell us about the rate at which an organism of interest is growing.
• A stem cell is an undifferentiated cell which can undergo division to produce many more similar cells, of which some will differentiate to have different functions.
• Embryonic stem cells form when an egg and sperm cell fuse to form a zygote and can differentiate into any type of cell in the body.
• Adult stem cells can be found in bone marrow and can form many types of cells including blood cells.
• Meristems in plants are found in root and shoot tips and can differentiate into any type of plant, and have this ability throughout the life of the plant.
• Therapeutic cloning involves an embryo being produced with the same genes as the patient.
• Myelin is produced by cells called Schwann cells.
• A stimulus is detected by receptors.
• Rod cells are more sensitive to light so they are better for seeing in low light, whereas cone cells allow colour vision.
• The pathway of stimuli is different from the usual response to stimuli, where the impulse does not pass through the conscious areas of the brain.
• Reflex arcs include pupils getting smaller to avoid damage from bright lights.
• In dim light, the circular muscles relax and the radial muscles contract making pupils larger- creates a better image.
• Eye defects occur when light cannot focus on the retina, such as short sightedness (myopia), long sightedness (hyperopia), cataracts, and colour blindness.
• Impulses are sent along a sensory neuron.
• The retina contains rod cells and cone cells, each of which convert light to nerve impulses destined for the brain.
• In the Central Nervous System (CNS), the impulse passes to a relay neuron.
• The eye has many different structures within it, including the retina, cornea, iris, ciliary muscles and suspensory ligaments, lens, and the process of accommodation.