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Biology CCEA AS Level 1.3 (Cells) 2024/2025 already graded A+
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Biology CCEA AS Level 1.3 (Cells) 2024/2025 already graded A+
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Biology CCEA AS Level 1.3 (Cells)How do you calculate the actual size of a cell? - ANSactual size = observed size/magnification
What are the two main types of microscope? - ANSOptical and electron
How do optical microscopes work? - ANSThey use glass lenses to focus visible light and as a
result has poor resolution
How do electron microscopes work? - ANSThe use electromagnetic coils to bend a beam of
electrons and as a result has a much higher resolution
What is a graticule? - ANSA scale which can be inserted into the eyepiece of the microscope
What specimens can be observed through an optical microscope? - ANSLiving specimens
(transparent ones must be stained)
What specimens can be observed through an electron microscope? - ANSDead, thin and
stained specimens
What are the two kinds of electron microscope? - ANS1. Transmission electron microscope -
works be passing beams of electrons through very thin slices
2. Scanning electron microscopes - bounce means of electrons off the surface of the object
What are the 2 types of cells? - ANSProkaryotic and Eukaryotic
What are the characterises of prokaryotic cells? - ANS- DNA not enclosed with a nuclear
membrane
- No membrane bound organelles
- Bacteria
What are the advantages of membrane bound organelles? - ANS- Larger membrane surface
area meaning the cell can contain more enzyme molecules and reaction rates can be increased
- All enzymes for particular process can be contained within one organelle
- Potentially harmful chemicals can be kept separate from rest of cell contents
What is the function of the slime capsule? - ANSTo protect the cell
What is the purpose of the flagellum? - ANSAids with movement of the bacteria
What is the nucleus? - ANS- Largest organelle
, - Contains DNA in the form of chromosomes
- Surrounded by double layer of membrane
- Control centre of the cell
What is the endoplasmic reticulum? - ANS- 3 dimensional membrane system enclosing
cisternae
- Extends throughout the cytoplasm
- Membrane is continuous with nuclear envelope
- Some has ribosomes attached and some does not (r.e.r and s.e.r)
- R.e.r. provides scaffolding for ribosomes to make proteins
- S.e.r. has many roles involving metabolism of lipids
What are ribosomes? - ANS- Small organelles
- Found free in cytoplasm or attached to rRNA
- Composed of larger and small sub-unit
- Site of protein synthesis
What is the golgi apparatus? - ANS- Series of cisternae lined by membranes
- Large number of vesicles entering and leaving apparatus
- Stores modifies and secretes chemicals produced by the cell
- Makes lysosomes
What are lysosomes? - ANS- Vesicles formed by the golgi apparatus
- Contain hydrolytic enzymes
- Thick membrane
- Fuse with material to be destroyed/digested to form a secondary lysosome
- Important role in phagocytosis
What are mitochondria? - ANS- Enclosed in a double membrane
- Filled with matrix
- Inner membrane folded into cisternae which project into the matrix, giving mitochondria a
greater SA
- Site of ATP production
What are microtubules? - ANS- Hollow cylinders made from tubulin protein
- Form part of the cytoskeleton
- Occur in centrioles which help form spindle fibres in cell division
- Also found in cilia and flagella
What is the cell wall? - ANS- Mainly composed of cellulose
- Cellulose molecules cross-linked together to form bundles called microfibrils
- In primary cell walls microfibrils are arranged randomly
- Cell walls of adjacent cells linked by middle lamella made largely of pectin
- Provide support
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