DA Bio Unit 2

• Osmosis is the movement of water from a dilute solution to a more concentrated solution through a selectively permeable membrane.
• When water enters the plant cell, water will pass into the vacuole by osmosis. The vacuole increases in volume and pressure which pushes against the cytoplasm. The cytoplasm pushes against the cell wall which stretches it making it turgid.
• If too much water leaves the cell then the cell membrane tears away from the cell wall which is called plasmolysis. A plasmolysed cell is very unlikely to recover.
• Transpiration is the evaporation of water from mesophyll cells followed by diffusion through the leaf air spaces and stomata.
• Temperature : In warmer conditions water evaportates faster.
• Wind : Evaporation is faster in higher wind speeds as the wind rapidly removes the evaporating water away from the stomata and leaf surface, thus maintaining a stepp gradient of moisture.
• Humidity: Humid conditions restrict evaporation, as there is a decrease in moisture gradient between the leaf surface and the surrounding air.
• Light intensity: Many plants close their stomata during darkness to reduce water loss.
• The surface area of leaves affects the rate at which transpiration takes place. The greater the surface area the greater the number of stomata, and the faster evaporation takes place.
• Plants use water for:

  • support
  • transpiration - the movement of water up through the plant
  • transport - as the water moves up through the plant it carries minerals
  • as a raw material for photosynthesis.
• Red blood cells transport oxygen and are adapted for this by containing haemoglobin that oxygen binds to. They have biconcave structures giving them a large surface area. They also dont have a nucleus so they can carry more haemoglobin.
• White blood cells provide a defence against disease.
• Lymphocytes produce antibodies.
• Phagocytes engulf and digest microorganisms by phagocytosis.
• Platelets help convert fibrinogen to fibrin in blood clotting. The fibrin forms a mesh to trap the blood and in the formation of scabs.
• Plasma is the liquid part of the blood. Its main function is transport of blood cells, food molecules, carbon dioxide, hormones and urea.
• An artery is a blood vessel that carries blood away from the heart. It has a thick wall which contains muscle for strength and elastic fibres that allow arteries to expant and recoil as blood pulses through. It has high blood pressure. It has no valves and the lumen diameter is relatively small.
• A vein is a blood vessel that carries blood back to the heart. It is thinner than an artery as there is less muscle and fewer elastic fibres. The blood pressure is low and it has valves to prevent the backflow of blood. The lumen diameter is relatively large.
• A capillary is a blood vessel that carries blood from arteries to veins. It is one cell thick to allow exchange between the blood and body cells. It has low blood pressure. No valves and its lumen diameter is very small.
• Regular exercise benefits the circulatory system in a number of ways. Exercise helps to strengthen the heart muscle and increase the cardiac output even when not exercising.
• Cardiac output is the volume of blood pumped by the heart per minute.
• DNA stands for deoxyribonucleic acid
• The genetic material is contained in the chromosomes in the nucleus of the cell.
• Chromosomes are genetic structures that occur in functional pairs in the nucleus of cells.
• Genes are a short section of DNA that codes for a particular characteristic.
• Genome is the entire genetic material found in an organism.
• Mitosis and meiosis are two different types of cell division.
• Mitosis is a type of cell division that produces cells genetically identical to the parent cell and to each other.
• Meiosis is a type of cell division that produces cells that have half the normal chromosome number.
• In mitosis daughter cells:

  • are identical to eachother
  • are identical to parent cell
  • produce two cells in one division
• In meiosis daughter cells:

  • Have half the number of chromosomes of parent cell
  • are different from eachother
  • produce four cells in two divisions
• An allele is a particular form of a gene e.g. brown eyes and blue eyes are different alleles of the eye colour gene.
• Homozygous describes the situation when both alleles of a gene are the same e.g. both alleles are for brown eyes.
• Heterozygous describes the situation when the two alleles of a gene are different e.g. one allele is for brown and the other is for blue eyes.
• A genotype are paired symbols showing the allele arrangement in an individual e.g. Rr
• A phenotype is the outward appearance of an individual e.g. round shape of the pea.
• Humans have 22 pairs of normal chromosomes and one pair of sex chromosomes.
• Male sex chromosomes are XY and female sex chromosomes are XX
• Genetic conditions are caused by a fault with genes or chromosomes.
• Haemophilia is a condition caused by a problem with the blood clotting mechanism. Sufferers are at risk of excessive bleeding.