This summary contains everything you need for the OCR Gateway GCSE exam, paper 1. It has all experiments, diagrams and notes but summarized. It is visually appealing and perfect for anyone that finds it easier to read notes when revising. There are pictures to help any visual learners and the notes...
Animal Cell
Nucleus
- Controls the activities of the cell.
- Contains the organism’s genetic material, arranged as chromosomes.
- Determines the cell’s appearance and function. Cytoplasm
- Contains instructions to make new cells or organisms Nucleus
Cell Membrane Cell Membrane
- Selective barrier.
- Controls which substances pass into and out of the cell. Mitochondria
- Also contains receptor molecules
Cytoplasm-
- Jelly-like substance.
- Chemical reactions, that keep the cell alive, happen here
Mitochondria
- Where respiration happens
- Special proteins (enzymes) enable glucose+ oxygen to react together
- The reactions transfer vital energy to the organ Plant Cell
Chloroplasts
- Contain green chlorophyll
- Chlorophyll transfers energy from the sun to the plant as light
- This is then used for photosynthesis
- Only found in the green parts of the plant Cytoplasm
Vacuole Nucleus
- This is full of cell sap Cell Membrane
- = watery solution of sugars and salts Cell Wall
- Helps keep the cell rigid Mitochondria
- So, it supports the plant and keeps it upright. Vacuole
Cell Wall Chloroplasts
- Surrounds the cell
- Made of a tough fibre called cellulose (peptidoglycan in bacteria)
- Makes the wall rigid and supports the cell
Genetic Material
- Floats freely in the cytoplasm
- One long strand of DNA = bacterial chromosome
Some Bacteria Cells
- Normally circular
Flagella (flagellum)
- Tail like structure lets cell move through liquids
Pili
Pili
- Tiny, ‘hair-like’ structures Cytoplasm
- Enable cell to attach to surfaces Cell Membrane
- Transfer genetic material between bacteria
Cell Wall
Slime Capsule
Slime Capsule
- Protects bacterium from drying out
Mitochondria
- Protects from poisonous substances
Genetic Material
- Helps bacteria to stick to smooth surfaces
Plasmid Plasmid
- Circular piece of DNA that stores extra genes
- Normally not needed for every-day survival but helps in times of stress
- Anti-biotic resistance is found here Flagella
Eukaryotic Cells = contain genetic material in a nucleus, they are complex and relatively large (10 –
100 micrometres), e.g. plant and animal cells.
Prokaryotic Cells = do not contain a nucleus, genetic material floats in the cytoplasm, typically
smaller than eukaryotic cells (1 – 10 micrometres), e.g. bacterial cells
,Bacteria
- Smallest living organisms
- Unicellular Organisms
- Each cell can carry out the 7 life processes (movement, respiration, sensitivity, growth,
reproduction, excretion, nutrition)
- Only around 1 micrometre
- Each is a different shape
- All contain a cell membrane, genetic material, cytoplasm and a cell wall
- Only some contain flagella, plasmids, slime capsules and pili
Total magnification = eyepiece lens magnification * objective lens magnification
Magnification = size of image/size of real object
Light Microscope
- To observe small structures in detail
- Passes light through an object, the lenses magnify the
object
- When you view though the eyepiece, you can see in more
detail
1. Place the sample on the slide
2. Place the slide on the stage
3. Make sure the lowest objective lens is over the
specimen
4. Use the course focusing knob to lower the objective
lens, to just above the slide, until you see your object
5. Look through the eyepiece and carefully use the fine
focusing knob to focus the image clearly
6. To see the cells in greater detail, switch to a higher magnification objective lens without
moving the stage. Use the fine focus knob to bring the object into clear focus again
Resolution = the smallest distance between two points that can be seen as separate entities
- You cannot see structures smaller than 0.2 micrometres with a light microscope
Staining a Cell
Many cells are colourless and so scientists stain them to make them easier to observe. Some stain
the whole cell and others highlight specific subcellular structures.
• Methylene blue – makes it easier to see the nucleus of an animal cell
• Iodine – makes it easier to see plant cell nuclei
• Crystal violet – stains bacterial cell walls
1. Place the cells on a glass slide
2. Add one drop of stain
3. Place a coverslip on top. Tap the coverslip gently with a pencil to remove air bubbles.
Light Microscopes Electron Microscopes
Cheap to buy and operate Expensive to buy and operate
Small and portable Large and difficult to move
Simple to prepare a sample Sample prep is complex
Natural colour of sample is seen unless staining is Black and white images are produced; false
used colour can be added to the image
Specimens can be living or dead Specimens are dead
Resolutions up to 0.2 micrometre Resolutions up to 0.1 nanometre
, Electron Microscopes
- Use electrons instead of light to produce an image
- Developed in the 1930s to allow scientists to see in
greater detail than ever before.
- The greater resolution is achieved by using high
energy electrons as the ‘light-source’.
Transmission Electron Microscopes (TEM)
- Produce the most magnified images
- Work in similar ways to a light microscope ; a beam
of electrons passes through a very thin slice of the
sample
- The beam is focused to produce an image
Scanning Electron Microscopes (SEM)
- Produces a 3 dimensional image of a surface
- They send a beam of electrons across the surface
of a specimen
- The reflected electrons are collected to produce an
image
Seeing Further
- The development of electron microscopy has allowed scientists to see the detail within
subcellular structures
- The TEM image shows that chlorophyll is stored in flattened membranes within a chloroplast.
(Left) Light microscope, (middle) TEM image, (right) SEM image of chloroplasts
DNA = in the nucleus of every eukaryotic cell
- Almost everyone’s DNA is unique. The only organisms that share identical DNA are identical twins
and clones
- DNA is arranged into sections
Chromosome = each long molecule of DNA (most people have 46 in each cell)
Genes = short sections that code for a characteristic (e.g. eye colour). The code that a gene contains
causes specific proteins to be made. The particular proteins determine the cell’s function. The
combination of genes in an organism controls how the organism functions and what it looks like.
Structure of DNA
- Made up of two strands joined together by bases
- The strands are then twisted together to form a double-helix
shape
- Made up of lots of small units called nucleotides which are
joined together. This makes DNA a polymer.
- Each nucleotide is made of a sugar (deoxyribose), a phosphate
and a base
- The two strands are held together by bonds between the bases
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