Cells and Control - Topic 2

  • Created by: aa_xx
  • Created on: 09-04-19 12:21

Sexual and Asexual Reproduction

  • Sexual reproduction involves the fusion of male and female gametes during the process of fertilisation
  • Because there are two parents, the offspring contain a mixture of their parents' genes i.e. the offspring differ genetically
  • In asexual reproduction there is only one parent. There is no fusion of gametes. The offspring are genetically identical to the parent - they are clones.
  • Asexual repoduction relies on mitosis
  • Many plants are able to reproduce asexually. This can occur in nature and man also uses this ability to artificially propagate plants
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Advantages and disadvantages of asexual reproducti


  • Only 1 parent is required
  • Many organisms can be produced quickly
  • All organsims are identical and will have chasen/desirable characteristics


  • There is a lack of variation - if conditions change all the offspring could die
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Mitosis summary

  • Multicellular organisms (consist of many cells) need to produce new cells to grow and for repair
  • Cells in multicellular organsims can be:

- Haploid - nucleus which contains 1 set of chromosomes e.g. gametes

- Diploid - nucleus which contains 2 sets of chromosomes e.g. body cells

  • The cell cycle consists of two stages: interphase and mitosis
  • DNA replication - this occurs when chromosomes in a cell mae copies of themselves before mitosis (cell division) occurs
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Mitosis summary 2

  • During mitosis a diploid (2n) cell splits to form two identical diploid (2n) cells
  • Mitosis is divided into 4 stages:

- prophase

- metaphase

- anaphase

- telophase

  • Cancer tumors form when cancer cells divide uncontrollably
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Stage descriptions

  • Prophase - the chomosomes are visible, the nucleus starts to break down, the spindle fibres appear
  • Metaphase - the chromosomes are lined up on the spindle fibres across the middle of the cell
  • Anaphase - the chromosome copies (chromatids) separate and move to either end of the cell, spindle fibres help them to move
  • Telophase - a cell surface membrane forms to separate the two cells (animal cells), this is called cytokinesis, cell walls form in plants.
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Cell differentiation

  • Red blood cell - transports oxygen, no nucleus to allow for more space for haemoglobin, large surface area to speed up diffusion
  • Fat cell - store energy as fat, cytoplasm is filled with large fat droplets, cells can expand, fat is stored for when body needs energy
  • Nerve cell - long fibre to carry electrical impulses around the body, many connections to other neurons
  • Muscle cells - allow muscles to contract to move bones, contain special contractile proteins that can shorten the cell to allow muscles to contract.
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  • Meritems - group of cells that divide rapidly by mitosis throughout the life of the plant
  • Meristems occur in the tips of shoots and roots
  • These undifferentiated cells elongate and differentiate to give rise to specialised cells with different structures and functions
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Growth in Plants

  • Palisade cells - Photosynthesis, contain many chloroplasts containing chlorophyll
  • Root hair cells - Absorb water and minerals, long extensions which increases the surface area for osmosis, diffusion and active transport
  • Guard cells - Open and close stomata, can change shape
  • Xylem vessels - Transport water and minerals, thickened walls to withstand water pressure, tiny pores in walls to allow water and mineral salts to leave the vessel, no cytoplasm (cell non-living) so water can move freely and end walls between cells are lost to form a tube.
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Stem Cells

  • Stem cell - an unspecialised cell that continues to divide by mitosis to produce new stem cells and other cells that differentiate into specialised cells
  • Embryonic stem cell - cell from an early stage of an embryo that can produce almost any kind of differentiated cell
  • Adult stem cell - stem cell found in specialised tissue that can produce more of that specialised tissue for growth and repair
  • i.e. can only produce a limited number of cell types e.g. blood stem cells in bone marrow can only produce the different types of blood cells
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Uses and Risks of Stem Cells


  • Bone marrow transplants
  • Type 1 diabetes treated
  • Replace damaged cells


  • Continued division of stem cells could cause cancer
  • Rejection - stem cells are destroyed by immune system of patient
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The Brain 1

Cerebral Cortex:

  • Divided into two cerebral cortex
  • Used for: memory, behaviour, consciousness, language and most senses including vision

Medulla Oblongata:

  • Controls heart and breathing rate
  • Responsible for reflexes e.g. vomiting, sneexing and swallowing
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The Brain 2

Spinal Cord:

  • Made of many nerves
  • Carries impulses from the brain to the rest of the body


  • Controls balance and posture
  • Coordinates timing and fine control of muscle activity
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CT scan:

  • Shows shapes and structures in the brain
  • Uses X-ray beams
  • Identifies tumors
  • See images in 'slices'
  • White areas show tumors
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Scanning 2

PET scan:

  • Shows brain activity
  • Injected with radioactive glucose (more active cells take in more glucose for respiration)
  • Uses gamma rays
  • Tells us how the brain works
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Spinal Cord Damage *

  • Damage to the spinal cord reduces the flow of information between the brain and parts of the body
  • Nerve damage in the lower spinal cord can cause loss of feeling in and use of the legs
  • Damage in the neck can cause quadrilplegia (loss of both arms and legs
  • There are no adult sten cells that can differentiate into neurons in the spinal cord and so new neurons cannot be made to repair damage
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Brain Tumours *

  • Cancer cells often divide rapidly to form a tumour
  • A brain tumour may squash parts of the brain and stop them working.
  • Tumours can be cut out or the cells can be killed using radiotherapy (high energy X-ray beams) and chemotherapy (injecting drugs that kill actively dividing cells)
  • All these methods can damage the body and brain, and chemotherapy may not work due to a blood-brain barrier - a natural filter that only allows certain substances to get from the blood into the brain (mainly due to cells in the capillary walls in the brain fitting together very closely)
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