B1 cell biology

• Eukaryotic cells contain their genetic material (DNA) enclosed in a nucleus
• eukaryote examples :

  Animal & plant cells
• Animal and plant cells both have cell membrane
• Bacteria cells are prokaryotes
• In prokaryotic cells, the genetic material (DNA) is not enclosed in a nucleus
• Prokaryotic cells are much smaller than eukaryotic cells
• Every order of magnitude is 10x greater than the one before
• Cytoplasm is a watery solution where chemical reactions take place
• Cell membrane controls the molecules that can enter and leave the cell
• Mitochondria is where aerobic respiration takes place
• Ribosomes are the sites of protein synthesis
• Chloroplasts contain chlorophyll and are the sites of photosynthesis
• The cell wall is made from cellulose, this strengthens the cell
• The vacuole is filled with a fluid called cell sap. Vacuole helps give the plant cell its shape
• Specialised cells have special adaptations to help them carry out their particular function. when cells become specialised, the process is called differentiation
• disadvantages of light microscopes:

  Limited magnification

  Limited resolution (cant see full detail)
• Advantages of electron microscope:

  • Greater magnification and resolution than light microscopes
• Magnification = size of image / size of real object
• In the nucleus, we find chromosomes , which are made of the molecule DNA
• chromosomes carry a large number of genes, which determine many of our features
• Cells have to be able to divide, called cell cycle
• Mitosis:

  1. The DNA replicates to form two copies of each chromosome. The cell grows and copies its internal structures
  2. One set of chromosomes is pulled to each end of the cell. This nucleus also divides
  3. The cytoplasm and the cell membrane divide to form 2 identical cells
• Functions of mitosis:

  1. mitosis is essential for growth and development of multicellular organisms
  2. Mitosis takes place when an organism repairs itself
  3. Mitosis happens during asexual reproduction
• diffusion is the spreading out of particles, resulting in a net movement from and area of higher concentration to an area of lower concentration
• The oxygen molecules move into the cell by diffusion from an area of higher concentration (outside the cell) to an area of low concentration ( inside the cell)
• Oxygen is used to generate energy for respiration, which produced the waste gas carbon dioxide
• There’s a higher concentration of CO2 inside the cell, than outside.

  the carbon dioxide moves out of the cell by diffusion
• Urea is a waste product produced inside cells. it diffused out of the cells into the blood plasma and is excreted by the kidneys
• Factors that affect diffusion:

  • concentration gradient (greater concentration gradient, faster diffusion)
  • temperature ( higher temp, more diffusion )
  • Surface area ( larger surface area , more diffusion)
• How does temp affect diffusion ?

  Higher temp means More kinetic energy, move faster so more diffusion
• Osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Cytoplasm is a relatively concentrated solution

  • if we place this cell in water, then osmosis will take place. water will move from outside the cell to inside the cell
  • Water moving in will cause the cell to expand and potentially burst
• If we place an animal cell in a very concentrated solution, water will move out the cell by osmosis and the cell will shrink
• if we place a plant cell in water, the water will move in by osmosis and the cell will expand

  The cell wall prevents the plant cell from bursting- cell becomes swollen (turgid)
• if we place a plant cell in a concentrated solution, the water will move out by osmosis, which will cause the cell to shrink ( cell has become flaccid)
• Active transport moves substances from a more dilute solution to a more concentrated solution (against the concentration gradient)
• How is active transport different from diffusion?

  active transport moves particles against the concentration gradient (diffusion moves down)

  active transport requires energy from respiration ( diffusion doesnt)