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.
State the function of ribosomes.
Contain ribosomal RNA and protein for protein synthesis.
State features of the cell wall.
- Consist of numerous polysaccharides, e.g. cellulose.
- Have a thin layer, the middle lamella, cementing adjacent walls together.
- Cellulose form microfibrils.
State the function of a cell wall.
- Provides mechanical strength, preventing the cell bursting under osmotic pressure.
- Gives mechanical strength to the plant as a whole.
- Allows water passage- contributes to movement of water through a plant.
State the function of cell vacuoles.
- Supports herbaceous plants by making cells turgid.
- The sugars and amino acids can act as a temporary food store.
- Pigments may colour petals to attract pollinating insects.
Explain what is meant by ‘tissue’.
A collection of similar cells aggregated together to perform a specific function.
Give an example of plant and animal tissue.
- Epithelial tissue
- Xylem tissue
Explain what is meant by ‘organ’.
An organ is a combination of tissues that are coordinated to perform a variety of functions, although they often have a predominant function.
Give an example of an organ system.
- Digestive system
- Respiratory system
- Circulatory system
Explain why an artery is described as an organ but a blood capillary is not.
An artery is made up of more than one tissue (epithelial muscle connective), whereas a blood tissue is only made up of one tissue (epithelial).
State the definition of a eukaryotic cell.
A cell that has a membrane-bound nucleus containing chromosomes. The cell also possesses a number of other membranous organelles, e.g. mitochondria and endoplasmic reticulum.
State the definition of a prokaryotic cell.
A cell of an organism lacking a nucleus and membrane-bound organelles.
State the definition of a protoplast.
The living portion of a plant cell, that is, the nucleus and cytoplasm along with the organelles it contains.
State the role of the capsule in a bacterial cell.
Protects bacterium from other cells and helps groups of bacteria to stick together for further protection.
State the role of the circular DNA in a bacterial cell.
Possesses genetic information for replication of bacterial cells.
State the role of the plasmid in a bacterial cell.
Possesses genes that may aid the survival of bacteria in adverse conditions, e.g. enzyme production that break down antibiotics.
Why are viruses not identified as ‘living cells’?
They cannot divide alone. They contain nucleic acids, DNA and RNA, enclosed within the capsid, but can only multiply when the attachment proteins on the capsid attach to a host cell.
Describe the products of mitosis
Produces two diploid daughter cells that have the same number of chromosomes as the parent cell and each other.
Describe the products of meiosis.
Produces four haploid daughter cells with half the number of chromosomes of the parent cell.
Describe the process of interphase.
The period in which the cell is not dividing.
Cell is actively synthesising proteins.
Prior to mitosis cell replicates.
Chromosomes invisible.
Describe the process of prophase.
- Chromosomes become visible.
- Nuclear envelope disintegrates.
- Nucleolus disappears
- Spindle fibres form from centrioles
Describe the process of metaphase.
Chromosomes line up at the centre of the cell.
Describe the process of anaphase.
- Spindle fibres attached to chromatids contract.
- Chromatids are pulled towards poles.
Describe the process of telophase.
- Chromosomes reach poles and become indistinct
- Nuclear envelope reforms
- Nucleolus reforms
- Spindle disintegrates
- Cell divides/cytokinesis
Cell division in prokaryotes occurs by binary fission.
Describe the process of binary fission.
- The circular DNA molecule replicates and both copies attach to the cell membrane
- The plasmids also replicate
- The cell membrane begins to grow between the two DNA molecules, pinching inward, dividing the cytoplasm into two
- A new cell wall forms between the two molecules of DNA , dividing the the original cell into two identical daughter cells, each with a single copy of the circular DNA and variable number of copies of the plasmid.
Describe the replication of viruses.
- Attach to host cell by attachment proteins
- Inject their viral nucleic acid into the host
- Genetic information in the acid provides instructions for the host cell to start producing viral components which are assembled into new viruses.
Describe the importance of mitosis
- Growth
- Repair
- Reproduction
List the three stages of the cell cycle
- Interphase
- Nuclear division
- Division of cytoplasm (cytokinesis)
How is cancer caused?
Result of damage to genes that regulate mitosis and the cell cycle- resulting in uncontrolled growth and division of cells.
How does chemotherapy disrupt the cell cycle in cancer treatment?
- Prevents DNA replication
- Inhibits metaphase by interfering with spindle formation
What problems are caused by chemotherapy?
Also disrupt cell cycle of normal cells, so fast dividing cells such as hair cells are damaged. Explains why hair loss is a result of chemotherapy.
