Cell Biology

• Cells can be either prokaryotic or eukaryotic. Eukaryotic cells are complex and include all animal and plant cells. Prokaryotic cells are smaller and simpler. e.g. bacteria
• Nucleus- contains genetic material that controls the activities of the cell.
• Cytoplasm- substance that is gel-like and where most chemical reactions take place. It contains enzymes.
• Cell membrane- holds the cell together and controls what goes in and out of the cell.
• Mitochondria- Where aerobic respiration takes place.
• Ribosomes- Site of protein synthesis in the cell.
• Cell wall- made of cellulose and supports the cell and strengthens it.
• Permanent vacuole- contains cell sap and is found in plant cells
• Chloroplasts- Where photosynthesis takes place. They contain chlorophyll which absorbs the light needed for photosynthesis.
• Bacteria cells don't have a nucleus instead they have a singular strand of DNA that floats freely in the cytoplasm.
• Bacteria can contain small rings of DNA called plasmids.
• Bacteria cells don't have chloroplasts or mitochondria.
• Light microscopes use light and lenses to form an image of a specimen and magnify it. They let us see individual cells and large subcellular structures, like nuclei.
• Electron microscopes use electrons instead of light to form an image and have a much higher magnification and resolution than light microscopes.
• Resolution is the ability to distinguish between two points , so a higher resolution gives a sharper image.
• You can calculate the magnification of an image using this formula:

  Magnification= image size/real size
• Differentiation is the process by which a cell changes to become specialised for its job.
• Most differentiation occurs as an organism develops. In most animal cells, the ability to differentiate is then lost at an early age, after they become specialised. However, lots of plant cells never lose this ability.
• Cells that have not yet differentiated are known as stem cells
• The function of a sperm cell is to get the male DNA to the female DNA.
• Adaptations of sperm cells:

  Has a long tail and streamlined head to help it swim to the egg.

  There are a lot of mitochondria in the cell to provide the energy needed.

  It also carries enzymes in its head to digest through the egg cell membrane.
• The function of the nerve cell is to carry electrical signals from one part of the body to another.
• Adaptations of nerve cells:

  The cells are long (to cover more distance) and have branched connections at their ends to connect to other nerve cells and form a network throughout the body.
• The function of a muscle cell is to contract quickly.
• Adaptations of muscle cells:

  The cells are long (so that they have space to contract) and contain lots of mitochondria to generate the energy needed for contraction.
• The function of the root hair cells is to absorb water and minerals from the soil.
• Adaptations of root hair cells:

  Grow into long hairs to give the plant a larger surface area for maximum absorption

  Have a thin cell wall to create a shorter diffusion path
• The function of phloem and xylem cells is to transport substances around the plant.
• Adaptations of xylem and phloem cells:

  To form xylem tubes and phloem tubes, the xylem and phloem cells are long and joined end to end.

  The xylem cells are hollow in the centre so stuff can flow through them.

  Similarly, the phloem cells have very few sub-cellular structures so the stuff can flow through them.
• Chromosomes are coiled up lengths of DNA molecules.
• Humans have a total of 46 chromosomes (23 pairs).
• 1st stage of the cell cycle (Growth & DNA replication)

  1. In a cell that's not dividing, the DNA is all spread out in long strings
  2. Before it divides, the cell has to grow and increase the amount of subcellular structures such as mitochondria and ribosomes.
  3. It then duplicates its DNA- so there's one copy for each cell. The DNA is copied and forms x-shaped chromosomes. Each 'arm' of the chromosome is an exact duplicate of the other.
• 2nd stage of the cell cycle (Mitosis)

  • The chromosomes line up at the centre of the cell and cell fibres pull them apart. The two arms of each chromosomes go to opposite ends of the cell
  • Membranes form around each of the sets of the chromosomes. These become the nuclei of the two new cells- the nucleus has divided.
  • Lastly, the cytoplasm and cell membrane divide forming two new daughter cells that contain the exact same DNA- they're identical.
• Prokaryotic cells reproduce by binary fission.
• Binary fission:

  1. The circular DNA and plasmids replicate
  2. The cell gets bigger and the circular DNA strands move to opposite 'poles' of the cell.
  3. The cytoplasm begins to divide and new cell walls begin to form.
  4. The cytoplasm divides and two daughter cells are produced. Each daughter cell has one copy of the circular DNA, but can have a variable number of copies of the plasmids.
• Bacteria can divide very quickly in the right conditions- a warm environment and lots of nutrients.
• The mean division time is the average amount of time it takes for one bacterial cell to divide into two.
• Embryonic stem cells have the ability to differentiate into any type of cell.
• Adult stem cells (bone marrow) can only differentiate into certain types of cells like blood cells.
• Adult stem cells from a healthy person can replace faulty blood cells in the patient who receives them.