A-Level Biology - OCR Questions With Correct Answers
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A-Level Biology - OCR
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A-Level Biology - OCR
A-Level Biology - OCR Questions With Correct Answers
What is a light microscope used for?
Observing living and dead specimins
What are the pros and cons of a light microscope?
Pros: Cheap, portable, easy to use, can study living specimens. Cons: Limited magnification, poor resolution.
What i...
A-Level Biology - OCR Questions With
Correct Answers
What is a light microscope used for?
Observing living and dead specimins
What are the pros and cons of a light microscope?
Pros: Cheap, portable, easy to use, can study living specimens. Cons: Limited
magnification, poor resolution.
What is a laser scanning confocal microscope used for?
Creating a high resolution, high contrast image, at different depths of the specimen.
What is a transmission electron microscope be used for?
Observing the internal ultrastructure of cells under high magnification and resolution
What is a scanning electron microscope used for?
Viewing the surface of objets under high magnification and resolution
What are the pros and cons of an electron microscope?
Pros: Very high magnification and excellent resolution. Cons: specimen has to be
dead, very expensive, very large, needs great skill and training to use.
What is the difference between a transmission and an scanning electron
microscope?
TEM sends a beam of electrons through the specimen, the SEM bounces electrons
off the surface.
What is the difference between light and electron microscopes?
Light uses lenses to focus a beam of light. Electron uses a beam of electrons,
focused by magnets.
What is an eye piece graticule?
A small ruler fitted to a light microscope's eyepiece. It must be calibrated using a
stage micrometer before being used to measure specimens.
What is a stage micrometer?
A millimeter long ruler etched onto a slide. it has 100 divisions, each of 0.01mm or
10 micrometers. It is used to calibrate the eyepiece graticule
Why do we stain specimens?
To provide more contrast, and make it easier to distinguish certain parts.
,What is differential staining?
Using a stain to distinguish between either 2 different orgaisms, or between
organelles of a specimin due to preferential absorbtion of stain.
What is the formula to calculate magnification?
Magnification = Image size / Actual size
What is the formula to calculate actual object size?
Actual size = Image size / Magnification
How do we work out image size?
Use a ruler and measure the image.
What is magnification?
A measure of how much larger the image of a specimen looks under the microscope
What is resolution?
The ability to distinguish between to adjacent individual points as separate.
What are the maximum resolutions of the different microscopes?
Light: 200nm; SEM: 10nm; TEM: 0.2nm.
What is the maximum magnification of the different microscopes?
Light: 1,500X; SEM: 100,000X; TEM: 500,000X.
What are the main structures of all eukaryotic cells?
Nucleus; nucleolus; cytoplasm; cytoskeleton; plasma membrane;mitochondria; Golgi
apparatus; smooth endoplasmic reticulum; rough endoplasmic reticulum; ribosomes.
What is the structure and function of the nucleus?
Surrounded by a double membrane (the nuclear envelope). Contains chromatin
(DNA wound around histones). Stores the human genome, controls the cell by
providing instructions for protein synthesis.
What is the structure and function of the nucleolus?
Made of RNA, produces ribosomes.
What is the structure and function of the nuclear envelope?
A double membrane embeded with channel proteins forming pores. Separates the
nucleus from the rest of the cell. Pores allow ribosomes and mRNA to leave the
nucleus.
What is the structure and function of the rough endoplasmic reticulum (RER)?
A system of fluid filled membranes studded with ribosomes. Continuous with the
nuclear membrane. Large surface area formed by folding, enables lots of protein
synthesis. Proteins pinched off in vesicles transported to the Golgi apparatus.
, What is the structure and function of the smooth endoplasmic reticulum
(SER)?
A system of fluid filled membranes. No ribosomes. Contain enzymes for cholesterol,
lipid and phospholipid synthesis.
What is the structure and function of the Golgi apparatus?
A stack of flattened membrane bound sacs. Vesicles from the RER join at the cis
face. Here they are modified, by adding sugar to make glycoproteins, adding lipids to
form glycolipids. Folding proteins into their 3D shape. Modified proteins are pinched
off from the trans face into transport vesicles.
What is the structure and function of the ribosomes?
2 subunits, large and small. Made of rRNA . Proteins synthesised here.
What is the structure and function of the mitochondria?
Double membrane bound. Inner membrane folded into cristae within a fluid filled
matrix. Contain own DNA and 70s ribosomes. Site of aerobic respiration.
What is the structure and function of the lysosomes?
Membrane bound sacs containing hydrolytic (digestive) enzymes. break down old
organelles and foreign matter for reuse.
What is the structure and function of the chloroplasts?
Double membrane bound. Inner membrane forms flat discs filled with chlorophyll
called thylakoids, in stacks called granum. These are surrounded by a fluid matrix
called the stroma. Contain own DNA and 70s ribosomes. Site of photosynthesis.
What is the structure and function of the plasma membrane?
Phospholipid bilayer, cholesterol, proteins, glycoproteins, glycolipids. Separates cell
contents from external environment. Controls what enters and leaves the cell.
Identifies cell as self. Acts as a receptor for various chemicals. site of chemical
reactions.
What is the structure and function of the centrioles?
Present in animals only. Two bundles of microtubules at right angles. Used as an
anchor point to separate chromosomes during cell division. Form the basis of cilia.
What is the structure and function of the cell wall?
Present in plants and fungi only. Bundles of cellulose fibres in plants. Chitin in fungi.
Provides support and strength, maintaining the cell's shape. prevents the cell from
bursting when turgid. Permeable to allow solutions through.
What is the structure and function of the flagella?
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