Cells and Control - Topic 2

• 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

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

• 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

• 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

• 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.

• 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.

• 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

• 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.

• 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

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

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

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

CT scan:

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

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

• 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

• 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)