CELL STRUCTURE

• examples of EUKARYOTIC cells are: animal cells, plant cells, fungal cells
• examples of PROKARYOTIC cells are: bacteria cells
• DNA in eukaryotic cells are found in a nucleus and formed as chromosomes
• prokaryotic cells don't have a nucleus. The DNA is loose in the cell
• Animals are multicellular so they are made up of many cells.
• Both plants and animal cells (EUKARYOTIC cells) have a cell membrane, cytoplasm, mitochondria, ribosomes and DNA enclosed in a nucleus. However plant cells have extra organisms such as a cell wall, vacuole and chloroplast
• Bacteria cells (PROKARYOTIC cells) are much smaller than eukaryotic cells. They have a cell wall, cell membrane, cytoplasm. The genetic material (DNA) is not enclosed in a nucleus, it is a single DNA loop and there may be more rings of DNA called plasmids
• In plant cell:

  • chloroplast: organelle that contains pigment called chlorophyll which absorbs light for photosynthesis
  • cell wall: its made from cellulose; strengthens and supports the plant
  • vacuole: filled with cell sap to help keep the cell turgid
• when cells become specialised it's called differentiation
• Example in animals: sperm cell is specialised to join with an egg cell, this is known as fertilisation (genetic information from the egg and sperm cell combine)
• • sperm cells have a long tail which allows it to swim to the egg cell
  • they have lots of mitochondria - provide energy needed to swim
  • contains enzymes at the tip of the head which allows them to digest their way through the outer layer of the cell
• Example in animals: Nerve cell is specialised o send electrical impulses around the body
• • nerve cells have synapses to allow the impulses to pass from one nerve to another
• Example in animals: Muscle cells are specialised to contract and have lots of mitochondria to provide energy for contraction
• Example in plants: Roots hair cells are specialised to increase the surface area of the root so it can absorb water and dissolved minerals.

  • they don't contain chloroplast - doesn't carry out photosynthesis
• Example in plants: Xylem is found in the plants stem and roots to carry water and dissolved minerals from the roots to the leaves
• Example in plants: Phloem transports dissolved sugars up and down the plant.

  • This is known as translocation
• cell differentiation is important because it allows for the development of specialised cells and tissues
• The cell cycle makes new cells for growth, development and repair
• Growth and DNA replication:

  1. before the cell divides, the cell grow and increases the amount of subcellular structures such as mitochondria and ribosomes.
  2. It then duplicates the DNA so there is a copy for each new cell. The DNA is copied and forms x-shaped chromosomes

  
• Mitosis (is a part of the cell cycle)

  1. The chromosomes line up at the centre of the cell and the cell fibres pull them apart. Each arm of each chromosome goes to the opposite end of the cell
  2. Membranes (that become the nuclei (nucleus)) form around each of the sets of chromosomes. It forms the nuclei of the two new cells - the nucleus has divided
  3. lastly, the cytoplasm and cell membrane divide

  The cell has now produced two new daughter cells - daughter cells contain exactly the same DNA (the cells are identical).

  DNA is identical to the parent cell
• a stem cell is an undifferentiated cell that can divide to produce more cells of the same type
• Embryonic Stem Cells can turn in ANY type of cell, but they are only found in early embryos
• differentiation is the process of a cell changing to become specialised for its job

  • undifferentiated cells (stem cells) can divide to produce lots more undifferentiated cells
• stem cells are found in early human embryos.

  • Adults also have stem cells found in bone marrow. Unlike embryonic stem cells, stem cells from bone marrow cannot turn into ANY cell type, only certain ones e.g blood cells
• Stem Cells in Plants:

  • they can differentiate to from any type of plant cell.
  • they are present throughout the lifespan of the plant
• Treatment with stem cells may be able to help conditions such as diabetes and paralysis.
• The use of stem cells has potential risks such as transfer of viral infection, and some people have ethical or religious objections.
• Risks of stem cell usage:

  • possible transfer of viral infection
  • ethical issues - involves destruction of human embryos
  • religious objections
• Stem cells from meristems in plants can be used to produce clones of plants quickly + economically:

  • rare species cloned to protect from extinction
  • crops with features e.g. disease resistance cloned to produce large numbers of identical plants for farmers