Cell Biology

• Eukaryotic cells:

  • Cells with genetic material (DNA) enclosed in a nucleus
  • Found in plant and animal cells
• Prokaryotic cells:

  • Cells with genetic material (DNA) not enclosed in a nucleus
  • Found in bacterial cells
  • Much smaller in comparison
• Genetic material in prokaryotic cells:

  • Consists of a single loop of DNA
  • May also have small rings of DNA called plasmids
• All eukaryotic or prokaryotic cells have:

  • DNA
  • Cytoplasm
  • Cell membrane
  • Ribosomes
• Order of magnitude:

  • A power to the base 10 used to quantify and compare size
  • 10 (10^1) times bigger = 1 order of magnitude bigger, 100 times (10^2) bigger = 2 order of magnitudes bigger
• Animal cell and plant cell sub-cellular structures:

  • Cell membrane: Controls movement of substances in and out of cell
  • Cytoplasm: Gel-like substance where chemical reactions take place
  • Nucleus: Contains genetic material (DNA) that controls activities of the cell
  • Mitochondria: Site of aerobic respiration, releases energy from glucose
  • Ribosomes: Site of protein synthesis
• Additional sub-cellular structures in plant cells:

  • Cell wall: Made of cellulose, strengthens cell
  • Chloroplasts: Contain chlorophyll to absorb light for photosynthesis to make glucose
  • Permanent vacuole: Filled with cell sap to help keep cell turgid/support plant
• Comparison of sub-cellular structures in eukaryotic and prokaryotic cells:

  • Animal cell: Cell membrane, cytoplasm, DNA, ribosomes
  • Plant cell: Cell membrane, cytoplasm, DNA, ribosomes, nucleus, mitochondria, cell wall, chloroplasts, permanent vacuole
  • Bacterial cell: Cell membrane, cytoplasm, DNA, ribosomes, plasmids
• Use a light microscope to observe, draw, and label a selection of plant and animal cells:

  • Must include a magnification scale
  • Prepare a microscope slide by peeling off a thin layer of tissue for plant cells or swabbing inside cheek for animal cells
  • Add a drop of stain and lower coverslip at an angle without trapping air bubbles
• How to view cells using a microscope:

  • Clip slide onto stage and turn on light
  • Select lowest power objective lens
  • Use coarse focusing dial to move stage close to lens
  • Adjust fine focusing dial to get clear image
  • Calculate total magnification of a microscope by multiplying magnification of eyepiece lens by magnification of objective lens
• Estimating cell sizes using a microscope:

  • Measure diameter of field of view and divide by number of cells that span field of view
• Rules of scientific drawing:

  • No sketching or shading, only clear, continuous lines
  • Include a magnification scale
  • Label important features like the nucleus
• Reasons for using a stain, thin layer of onion tissue, and lowering cover slip at an angle:

  • Stain: Makes sub-cellular structures visible
  • Thin layer of onion tissue: Allows light to pass through
  • Lowering cover slip at an angle: Avoids trapping air bubbles
• Safety measures during cell collection:

  • Wear gloves or wash hands to prevent irritation from stain
  • Disinfect work surfaces and dispose of used swabs to prevent infection spread
• To observe structures within a cell in greater detail:

  • Use a higher power objective lens or an electron microscope (not accessible to students)
• Saprotrophic nutrition


  A special type of heterotrophic nutrition used by fungi, where they secrete digestive enzymes out of their body onto the food, break it down, and then absorb the small nutrients into their cells
• Features of Animals


  • Reproduce sexually
  • Multicellular
  • Heterotrophs
• 5 Kingdoms of Life

  • Bacteria
  • Fungi
  • Animals
  • Plants
  • Protoctists
• Bacteria can only live in a few specific environments-False
• Magnification


  How many times larger the image is than the object
• Light path through a microscope

  Light source->stage->microscope slide->object->objective lens->body tube->eyepiece lens->eye
• Mitosis and Cytokinesis


  1. DNA condenses to form chromosomes

  2. Chromosomes line up along the centre of the cells

  3. Cell fibres pull the two arms of each chromosome to opposite sides (poles) of the cell

  4. Cytokinesis - the entire cell divides to form two identical daughter cells
• Reasons why new cells are required

  • Growth
  • Development
  • Repair
• Cell Cycle


  The series of steps that take place as a cell grows and then divides
• Steps of the Cell Cycle

  1. Cellular growth - the cell gets larger and produces more sub-cellular structures

  2. DNA replication - chromosomes duplicate

  3. More cell growth

  4. Mitosis - the DNA divides into two

  5. Cytokinesis - the cell divides into two
• Fertilisation and embryo development

  1. When a sperm cell fertilises an egg cell they form a single cell called a zygote

  2. This cell then divides by mitosis to form a ball of cells which we call an embryo

  3. The cells in this embryo are known as embryonic stem cells and can differentiate into any type of cell
• Sperm cell

  • It has half as much genetic material as a normal cell
  • It has lots of mitochondria to provide the energy for movement
  • It has a flagellum to allow it to swim to reach the egg
  • It is streamlined to make swimming easier
  • It has digestive enzymes in its head to break through the wall of the egg
• Stem Cell Treatment


  1. Extract embryonic stem cells from early embryos

  2. Grow them in a laboratory

  3. Stimulate them to differentiate into whichever type of specialised cell that we want

  4. Give them to the patient to replace their faulty cells
• Drawbacks of using embryonic stem cells in stem cell therapy

  • Stem cells have a limited supply
  • The risk of rejection
  • Ethical issues associated with stem cells
  • Potential life
• Advantages and Disadvantages of Adult Stem cells

  • Adv:Adult stem cells are taken from the patient so are not in limited supply
  • Adv:Adult stem cells won't cause rejection as they're taken from the patient themselves
  • Disadv:Adult stem cells have to be extracted from the bone marrow which is very painful
  • Disadv:Adult stem cells can only differentiate into a few cell types
• Risks of using stem cells in medicine

  • The stem cells could be infected with a virus whilst in the laboratory, which could then infect the patient
  • As stem cells divide quickly, there is a chance they could divide uncontrollably once they've been transplanted, and then develop into a tumour
• Molecules able to diffuse in and out of cells

  • Water
  • Glucose
  • Amino Acids
• Factors that affect the rate of Diffusion

  • Concentration Gradient
  • Temperature
  • Surface Area
  • Distance to diffuse across
• Why does a higher temperature increase the rate of diffusion?

  Higher temperature means particles have more (kinetic) energy. So they move around faster And can diffuse more quickly
• Osmosis


  The net movement of water molecules across a partially permeable membrane, from a region of high water concentration, to a region of low water concentration
• If red blood cells are placed in pure water, the water concentration would be higher outside the cell than inside, so water would move down its concentration gradient into the cell, causing it to swell and possibly burst
• Active transport


  The movement of molecules across a membrane, from a region of low concentration to a region of h concentration, which requires energy from respiration
• Examples of exchange surfaces in humans

  • Alveoli (or lungs)
  • Villi (or small intestines)
• Exchange Surface


  A part of an organism over which substances are exchanged with the environment
• The small protrusions of the lining of the small intestines are called villi. These have a large surface area which increases the area over which we can absorb nutrient molecules.