B3
- Created by: IrishEllie98
- Created on: 10-06-14 09:04
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- B3
- Cell Division
- Becoming Multicellular
- Humans are multicellular. The advantages of being multicellular are:
- It allows an organism to become larger and more complex
- It allows different cells to take on different jobs, which is known as 'Cell Differentiation'
- When an organism becomes multicellular, it needs systems that can:
- Allow communication between all cells in the body
- Supply all cells with enough nutrients
- Control exchanges with the environment such as heat and gases
- Humans are multicellular. The advantages of being multicellular are:
- Mitosis
- The process that produces cells for growth
- Cells made are genetically identical
- Before cells divide, DNA replication must take place in order for each cell to have 2 copies of each chromosome
- Body cells in mammals have 2 copies of each chromosome, so are diploid cells
- Before mitosis happens, DNA must be replicated. This involves:
- 2 strands of DNA molecule 'unzipping' to form single strands
- new double strands form by DNA bases lining up in complementary pairings
- Mitosis occurs:
- Chromosomes line up along the centre of the cell and divide. The copies then move to the opposite poles (ends) of the cell.
- Meiosis
- Type of cell division which produces gametes.
- Gametes are haploid cells because they contain only one chromosome from each pair
- This means that the zygote only receives one copy of a gene from one parent and another copy from the other parent
- Producing 'Genetic Variation'
- This means that the zygote only receives one copy of a gene from one parent and another copy from the other parent
- The structure of a sperm cell is adapted to its function. It has:
- many mitochondria, to provide energy for swimming to the egg
- an acrosome which releases enzymes to digest the egg membrane
- In meiosis, there are 2 divisions:
- First the single chromosomes are joined to form X shaped chromosomes, and chromosomes with the same genes pair up. Then:
- In the first division: 1 chromosome from each pair move to opposite poles of the cell
- In the second division: the copies of each chromosome come apart and move to opposite poles of the cell
- First the single chromosomes are joined to form X shaped chromosomes, and chromosomes with the same genes pair up. Then:
- Becoming Multicellular
- Respiration
- The incomplete breakdown of glucose, resulting in the build up of lactic acid, is known as oxygen debt
- C6H12O6+ 6O2 = 6CO2+6H2O
- Aerobic Respiration
- Measuring Respiration rate
- Respiratory Quotient
- RQ= CO2 Produce/O2 Used
- Experiments to measure the rate of respiration
- Measure the amount of O2 used up
- The faster it's consumed, the faster the respiration rate
- Measure the rate that CO2 is made
- Measure the amount of O2 used up
- Metabolic Rate
- The sum of all reactions which occur in the body
- If the metabolic rate is high, more O2 is needed, as aerobic respiration is faster
- Changes in temperature and pH also affect the rate of respiration, as they affect enzymes, which control respiration process
- Respiratory Quotient
- Disadvantages on Anaerobic respiration
- 1) The lactic acid made and built up in muscles causes pain and fatigue. 2) Releases much less energy per glucose molecule
- Glucose = Lactic acid (+energy)
- Anaerobic Respiration
- Releases energy from food and this is trapped in a molecule called ATP
- During exercise, despite an increase in breathing rate and heart rate, the muscles do not receive sufficient oxygen
- Respire anaerobically in addition to aerobically
- Cell Division
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