3. Cell Structure Flashcards
Distinguish between magnification and resolution.
Magnification is how many times bigger the image is compared to the real object. Resolution is the minimum distance apart that two objects can be in order for them to appear as separate items.
An organelle that is 5 μm in diameter appears under a microscope to have a diameter of 1mm. Calculate how many times the organelle has been magnified.
200 times.
1 mm= 1000 μm
A ribosome is typically 25nm in diameter. Calculate its diameter when viewed under an electron microscope magnified 400000x
10mm
(0.000025 × 400000)
(Image size= actual size x magnification)
At a magnification of x12000 a structure appears to be 6mm long. Determine its actual length.
500nm
(6000000/12000)
(Actual size= Image size/magnification)
Explain how the electron microscope is able to resolve objects better than the light microscope.
The electron microscope uses a beam of electrons that has a much smaller wavelength than light.
Explain why specimens have to be kept in a vacuum in order to be viewed effectively using an electron microscope.
Electrons are absorbed by the molecules in air and, if present, this would prevent the electrons reaching the specimen.
In practice, the theoretical resolving power of an electron microscope cannot always be resolved. Explain why not.
The preparation of the specimens may not be good enough.
A higher energy electron beam is required and this may destroy the specimen.
State the differences between the transmission electron microscope and the scanning electron microscope.
TEM has higher resolution and magnification than SEM.
TEM has the electron beam passed through thin sample. Electrons pass through the dense parts of the sample less easily, creating contrast forming a 2D image.
SEM has the electron beam directed at sample, but the electrons bounce off the surface of the specimen, forming a final 3D image.
What equipment is used to calibrate the eyepiece graticule?
A stage micrometer.
List three carbohydrates that are absorbed by an epithelial cell of the small intestine.
Glucose, fructose and galactose.
State organelles that might be numerous in a sperm cell.
Mitochondrion
Nuclei
Acrosomes
State organelles that might be numerous in a white blood cell.
Golgi apparatus
Lysosomes
State organelles that might be numerous in a liver cell that manufactures proteins and lipids at a rapid rate.
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
Ribosomes
Mitochondria
Describe the structure of the nucleus.
Nuclear envelope- controls entry/exit of materials and controls reactions within it.
Nuclear pores- allow passage of large molecules out of the nucleus, e.g mRNA.
Nucleoplasm- bulk of nucleus.
Chromosomes- consist of protein bound DNA
Nucleolus- manufactures ribosomal RNA and assembles ribosomes.
State the functions of the nucleus.
- Acts as control centre of the cell.
- Retains genetic material of the cell.
- Manufactures ribosomes and ribosomal RNA.
Describe the structure of the mitochondria.
- Double membrane- surrounds the cell, controlling the entry and exit of material.
- Cristae- extension of inner membrane. Provides large surface area for attachment of enzymes and proteins involved in respiration.
- Matrix- contains proteins, lipids, ribosomes and DNA that allows mitochondria to control the production of their own proteins. Enzymes found for respiration.
State the functions of the mitochondria.
- Site of aerobic respiration.
- Produce ATP, from respiratory products, e.g. glucose.
Describe the structure of the chloroplast.
- Chloroplast envelope- Controls what enters/leaves chloroplast, double plasma.
- Grana- stacks of thylakoids containing chlorophyll. Where light absorption occurs.
- Stroma- matrix where synthesis of sugars takes place.
How is the structure of chloroplasts adapted for photosynthesis?
- Granal membranes provide a large surface area for the attachment of chlorophyll, enzymes and electron carriers for light absorption.
- Fluid of stroma provides all the enzymes needed to synthesise sugars.
- Chloroplasts contain both DNA and ribosomes so they can quickly manufacture proteins needed for photosynthesis.
Describe how the rough endoplasmic reticulum is adapted for its function.
- Provide a large surface area for synthesis of proteins and glycoproteins.
- Provide a pathway for transport of materials, especially proteins throughout the cell.
Describe the functure of the smooth endoplasmic reticulum.
- Synthesise, store and transport lipids.
- Synthesise, store and transport carbohydrates.
Describe the functions of the Golgi apparatus.
- Add carbohydrates to proteins to form glycoproteins.
- Produce secretory enzymes.
- Secrete carbohydrates.
- Transport, modify and store lipids.
- Form lysosomes
State the functions of lysosomes.
- Hydrolyse material ingested by phagocytic cells.
- Release enzymes to the outside of the cell (exocytosis) to destroy material around the cell.
- Digest worn out organelles so they can be re-used.
- Break down cells after they have died.
What are the two different types of ribosomes?
80S- found in eukaryotic cells.
70S- found in prokaryotic cells, mitochondria and chloroplasts.
