Biology

• What are the two types of organisms?

  Eukaryotes and prokaryotes.
• What are eukaryotes?


  Eukaryotes (animal and plant cells) are made from complex cells called eukaryotic cells. They have a nucleus.
• What are prokaryotes?


  Prokaryotes (e.g. bacteria) are smaller and simpler cells called prokaryotes. These have no nucleus and the genetic material is in the cytoplasm.
• What are sub-cellular structures?


  Parts of the cell that each have a specific function (e.g. chloroplasts, mitochondria, cell wall etc...)
• What are the structure in eukaryotic cells?

  Nucleus, cytoplasm, mitochondria and cell membrane (and cell wall and chloroplasts if a plant).
• What are the structures in prokaryotic cells?

  Chromosomal DNA, plasmids and cell membrane.
• What is the nucleus and it's function?

  Nucleus contains DNA (genetic material) in the form of chromosomes that control the cell's activities.
• What is the cytoplasm and it's function?

  Cytoplasm - gel-like substance where most of the chemical reactions happen.
• What is the mitochondria and it's function?

  These are the site of cellular respiration and contain the enzymes needed for the reactions involved.
• What is the cell membrane and it's function?

  Cell membrane holds the cell together and controls what goes in and out by providing a selective barrier. They also contain receptor molecules that are used for cell communication, e.g. by hormones.
• What is the rigid cell wall and it's function?

  The cell wall is made of cellulose and gives support for the cell.
• What are the chloroplasts and their function?

  They're where photosynthesis occurs. They contain a green substance called chlorophyll.
• What is the chromosomal DNA and it's function?

  Chromosomal DNA (one long circular chromosome) controls the cell's activities and replication. It floats free in the cytoplasm (not in the nucleus).
• What are plasmids and their function?

  They are small loops of extra DNA that aren't part of the chromosome. Plasmids contain genes for things like drug resistance, and can be passed between bacteria.
• What is the cell membrane in bacteria and its function?


  Controls what goes in and out. The cell is also supported by a cell wall.
• What do microscopes use to magnify images?

  Lenses to magnify images (make them look bigger). Microscopes also increase the resolution (they increase the detail you can see).
• What is resolution?


  How well a microscope distinguishes between two points that are close together.
• When were light microscopes invented and what do they do?

  In 1590s. They let us see things like nuclei and chloroplasts.
• When were electron microscopes invented and what do they do?

  In 1930s. They let us see much smaller things in more detail like the internal structure of mitochondria. This has allowed us to have a much greater understanding of sub-cellular structures. Only electron microscopes will let us see things as tint as plasmids and viruses.
• What are the pros and cons of Transmission electron microscopes (TEMs).

  Pros - higher magnification and resolution than light microscopes

  Cons - Not portable, expensive, complicated process to prepare specimens for use (they can't be used to look at living tissues, unlike light microscopes)
• What does the light microscope look like?

  
• What is the eyepiece lens and it's function?


  Looked through to see.
• What is the objective lens and it's function?

  Magnifies the image. Usually there are three difference objective lens (e.g. x4, x10, x40).
• What is the stage and it's function?

  Supports the slide.
• What is the clip and it's function?

  Holds the slide in place.
• What is the handle and it's function?

  To carry the microscope with.
• What is the lamp and its function?

  Shines light through the slide so the image can be seen more easily.
• What are the focusing knobs and their function?

  Move the stage up and down to bring the image into focus.
• Why do you need to take a thin piece of your specimen to start with?


  So your specimen can let light through it (so it can be seen clearly).
• What are the steps to preparing the specimen before the investigation?

  1) Thin slice of specimen.

  2) Take a clean slide (clear glass/plastic) and use a pipette to put one drop of water or mountant (a clear, gloopy liquid) in the middle of it - this will secure the specimen in place.

  3) Use tweezers to place your specimen on the slide.

  4) Add a drop of strain if needed (if specimen is transparent/colourless) so that it can be seen easier . Different stains highlight different structures/tissues (eosin stains cytoplasm, methylane blue stains DNA).

  5) Place a cover slip (square of thin transparent glass/plastic) at one end of the specimen, holding it at an angle with a mounted needle.

  6) Lower the cover slip onto slide. Press down gently with needle so that there are no air bubbles trapped beneath it.
• What are the steps to viewing the specimen?

  1) Clip the slide containing your specimen onto the stage

  2) Select lowest-powered objective lens (least magnification).

  3) Use coarse adjustment knob to move stage up to just below the objective lens. Looking down eyepiece, move the stage downwards until specimen is just about in focus.

  4) Adjust the focus with the fine adjustment knob, until you get a clear image of your specimen.

  5) If you need to see your specimen with greater magnification, swap to a higher powered objective lens and refocus

  Once happy, produce scientific drawing.
• Why is a higher magnification not always a good thing?

  If your specimen is relatively big, you might not be able to see the whole thing. It can also be difficult to focus at high magnifications.
• What is magnification?


  How many times bigger the image is than its real size?
• How do you work out total magnification?

  total magnification = eyepiece lens magnification x objective lens magnification
• How do you work out general magnification?

  magnification = image size/real size
• How many micrometres in a milimetre?

  1000 micrometres (μm) = 1 milimetre (mm)
• Why may you have to work in standard form?

  Because microscopes can see such tiny objects sometimes it's useful to write numbers in standard form because they're so small.
• What does DNA contain?

  All of an organism's genetic material - the chemical instructions it needs to grow and develop. It is a double helix of paired bases. DNA is arranged into chromosomes.
• What are chromosomes?

  Long molecules of coiled up DNA. The DNA is divided up into short sections called genes.
• What is the structure of DNA?

  DNA is a double helix (a double-stranded- spiral). Each of the two DNA strands is made up of lots of nucleotides joined together in a long chain - this makes DNA a polymer.