topic 1 key concepts of biology

• The structure of cells can be studied using a light microscope
• Light microscopes shine light on the specimen (i.e the cell to be studied)
• The image is then passed through lenses and magnified (i.e made bigger)
• Different parts of a cell can be seen by staining the cell before observing under the microscope
• The detail obtained from a microscope depends on its resolution. The better/higher the resolution, the clearer the image
• Ocular (Eyepiece Lens) is used to observe the magnified object
• Objective Lens provides stronger lenses that offer greater image magnifications
• Coarse adjustment knob/focusing wheel is used to focus the image for a sharper, clearer image
• Fine adjustment knob/focusing wheel is used to finely adjust the image focus for a sharper, clearer image
• Light is necessary for a brighter, clearer image observation
• Stage is a platform to rest the slide and specimen
• Stage Clips are used to hold the slide and specimen steady
• Magnification can be calculated using the image size and the actual size
• Magnification questions often ask for pupils to convert between units and use standard form
• Most cell magnification questions MUST be converted into micrometres
• Scale bars are shown on micrographs and can be used to estimate sizes
• The scale bar in the picture is 2um. The entire micrograph is approximately 2x the scale bar, so the micrograph is 4um
• Field of View (FOV) is the diameter of the circular area visible under the microscope
• Calculated by multiplying the magnification of the eyepiece lens by the magnification of the objective lens
• Plant and animal cells have some features in common
• Cell membrane separates the contents of the cell and its surroundings, controls the movement of substances into and out of the cell
• Cytoplasm is where many of the cell’s chemical reactions take place and contains many organelles
• Nucleus is an organelle that contains DNA, controls all the activities of the cell
• Mitochondria are organelles where aerobic respiration takes place
• Ribosomes are the site of translation for protein synthesis
• Plant cells have additional structures
• Cell wall is made of tough cellulose, supports the cell and gives it shape
• Large permanent vacuole is filled with cell sap, helps support plants by keeping cells turgid
• Chloroplasts are organelles that contain chlorophyll, used for photosynthesis
• Specialised cells have a particular function
• There are 216 different cell types in the human body, all with the same basic design but adapted for their specific function
• Red Blood Cells contain haemoglobin that binds to oxygen and are biconcave to increase the rate of oxygen diffusion
• Small intestine Cells have microvilli to increase the surface area for food absorption
• Pancreatic Cells produce enzymes required in the small intestine to break down food, have a large number of ribosomes for protein synthesis
• Sperm Cells have :

  • acrosome : contains digestive enzymes to break down the jelly like layer surrounding the egg cell ,so the head of the sperm can fuse with the egg cell membrane
  • haploid nucleus ; contains half the genetic information so that when the nuclei fuses with the ovum a full chromosome complement is established
  • , mitochondria : to provide the cell with energy from respiration for it to move to the egg cell
  • flagella for movement towards the egg cell
• Egg Cells have

  • a cell membrane: controls the movement of substance into and out of the cell and becomes hardened following fertilisation to prevent other sperm entering the egg
  • haploid nucleus
  • large cytoplasm : contains nutrients to supply the fertilised egg with a source of energy and raw material for the growth and development of the embryo
  • jelly coat (zona pellucida ): protects the egg cell and also hardens following fertilisation to prevent other sperm entering the cell
• Core Practical 1 – Investigating Biological Specimens
• Method 1 involves viewing pre-prepared slides and calculating total magnification and field of view diameter
• Method 2 includes preparing and viewing plant cells using iodine (to stain the cell )solution and a microscope slide
• Safety precautions include lowering the coverslip carefully to avoid air bubbles and disposing of human cells in disinfectant