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
1 of 16

Advantages and disadvantages of asexual reproducti

Advantages:

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

Disadvantages:

  • There is a lack of variation - if conditions change all the offspring could die
2 of 16

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
3 of 16

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
4 of 16

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.
5 of 16

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.
6 of 16

Meristems

  • 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
7 of 16

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.
8 of 16

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
9 of 16

Uses and Risks of Stem Cells

Uses:

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

Risks:

  • Continued division of stem cells could cause cancer
  • Rejection - stem cells are destroyed by immune system of patient
10 of 16

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
11 of 16

The Brain 2

Spinal Cord:

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

Cerebellum:

  • Controls balance and posture
  • Coordinates timing and fine control of muscle activity
12 of 16

Scanning

CT scan:

  • Shows shapes and structures in the brain
  • Uses X-ray beams
  • Identifies tumors
  • See images in 'slices'
  • White areas show tumors
13 of 16

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
14 of 16

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
15 of 16

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)
16 of 16

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Cells, tissues and organs resources »