Section 2 - Unit 3: Cell Structure Flashcards
Process of TEM
1) electron gun produces a beam of electrons that is focused on specimen by a condenser electromagnet
2) the specimen absorbs some electrons to appear dark and in other areas, the electrons pass straight through, looking bright
3) an image known as a photomicrograph is produced
Process of SEM
1) a beam of electrons is focused on the specimen from below
2) the electrons are scattered by the specimen and the pattern of scattering depends on the contours of the specimen
3) from this, a 3D image is built
Advantages of using a SEM
- specimens do not have to be extremely thin
- 3D images are created automatically
Why is the resolution not necessarily achieved in electron microscopes? (1)
- High resolution requires a higher energy electron beam and this can sometimes destroy the actual specimen
Eye Piece Graticule
A glass disc placed in the eyepiece of a microscope which has a printed scale from 0 to 100 on it
Differences between eukaryotic and prokaryotic cells
- membrane bound organelles vs non-membrane bound organelles
- mitosis/meiosis vs binary fission
- multicellular vs unicellular
Explain the advantages and the limitations of using a TEM to investigate cell structure (5 marks)
- Higher resolution due to shorter wavelength of electrons
- so structure of organelles can be seen
- In a vacuum so living specimens cannot be viewed
- Cells must be extremely thin so that the beam of electrons pass through
- Doesn’t produce a colour image even though there’s an extremely complex staining process
Explain why it’s important for the cell specimen to be thin in microscopes (2 marks)
- Only a single layer of cells is needed
- So that light can pass through
Explain why the solution should be ice cold in centrifugation (1 mark)
- To slow the enzymes and prevent them from denaturing the organelles
Describe how the length of the cell could be estimated in an optical microscope (2 marks)
- The length of the cell could be measured with an eyepiece graticule
- And then calibrated against a stage micrometer
Explain the function of stroma in a chloroplast (1 mark)
- It contains enzymes for a light independent reaction
Explain the function of granum in a chloroplast (1 mark)
- Contains chlorophyll molecules to trap light for a light dependent reaction
Explain the advantage of the width of mitochondria being no more than 1μm (1 mark)
- There’s a shorter diffusion pathway
Explain why large numbers of Golgi apparatus and mitochondria are found in mucus-secreting cells (2 marks)
- Golgi Apparatus adds sugars to proteins
- Mitochondria provides ATP for this process
Explain why viruses are not considered living (3 marks)
- Cannot reproduce independently
- They have no nucleus, plasma membranes, cytoplasm or ribosomes
- They are not made of cells
Describe the position of the protein components in a eukaryotic cell membrane (2 marks)
- Either integral (across the entire bilayer)
- Or extrinsic (only on one side of the bilayer)
Describe cholesterol and its role in a phospholipid bilayer (2 marks)
- Acts as a buffer for membrane fluidity
- At high temperatures, it prevents fluidity from rising too high, and at low temperatures, it prevents the membrane from becoming solid
Describe the structure and function of the cell-surface membrane (3 marks)
- Phospholipid bilayer
- With hydrophilic head and hydrophobic tail
- Regulates the transport of substances
Describe the structure and function of the nucleus (6 marks)
- Surrounded by a nuclear envelope
- Which acts as a semi-permeable double membrane
- Nuclear pores
- Which allows substances to enter/exit
- A dense nucleolus made of RNA and proteins
- Which assemble ribosomes
Describe the function of the Golgi Apparatus
- Processes and packages proteins and lipids
- Produces lysosomes
(classrooms that package and store materials)
Describe the structure of Golgi Apparatus
- Series of fluid filled, flattened & curved sacs with vesicles surrounding the edges
Describe the functions of a cell wall
- Provides mechanical strength
Describe the structure of a cell wall
- Microfibrils of the polysaccharide cellulose embedded in a matrix
Describe the functions of RER
- Folds and processes proteins made on the ribosomes
- Suitable for protein synthesis
Describe the structure of RER
- Series of flattened sacs enclosed by a membrane with ribosomes on the surface
Describe the structure of mitochondria
- Oval shaped, bounded by a double membrane called the envelope
- Inner membrane - folded to form projections called cristae with a matrix on the inside for the attachment of enzymes and protein
Mitochondria is like the mail - has the info (energy) needed for the cell in an envelope (double membrane). Inside is the actual Clear Message (Cristae + Matrix)
Describe the function of mitochondria
- Site of respiration
- Responsible for the production of ATP
- Matrix contains all the enzymes needed for respiration
Describe the function of cytoplasm
- Site of metabolic reactions
- Contains all organelles
Describe the structure of SER
- System of membrane bound sacs
Describe the function of SER
- Synthesises, stores and transports lipids and carbohydrates
Smooth ER - Like a slide (synthesises/stores) that transports children (carbs) and their lego (lipids)
What is the name of the fluid-filled membrane sacs found within the chloroplasts?
- Thylakoids
Which cell type is between 0.1 and 5.0 micrometres in diameter?
- Prokaryote
Describe the function of a chloroplast (2 marks)
- Absorbs sunlight
- For photosynthesis
Explain two ways in which fatty acids are important in the formation of new cells (2 marks)
- Fatty acids used to make phospholipids;
- Meaning that more membranes can be made
- Fatty acids respired to release energy
- Energy used for cell production
Explain the role of a centromere (2 marks)
- Holds the chromatids together
- Attaches the chromatids to the spindle
Explain two reasons why mitosis is important in cells (2 marks)
- Growth in the number of cells
- So replaces cells in the body
Give two processes which occur during interphase that enable cell division to occur (2 marks)
Any two from:
- Increase in number of organelles
- DNA replication
- Increase in volume of cytoplasm
- ATP synthesis
Give one way in which a benign tumour differs from a malignant tumour (1 mark)
- Benign does not cause cancer
Describe two ways in which both types of tumour may cause harm to the body (2 marks)
Any two from:
- May damage a specific organ
- May cause blockages
- May damage / exert pressure on other organs
Describe the behaviour of chromosomes during mitosis and explain how this results in the production of two genetically identical cells (7 marks)
- Chromosomes shorten and thicken
- Chromosomes replicate to form two identical chromatids
- Chromatids move to the equator
- And attach to individual spindle fibres
- The spindle fibres contract/centromeres divide
- Chromatids move to opposite ends of the spindle
- Each pole receives identical copies of each chromosome
- A nuclear envelope forms around each group of chromosomes
sethu if you got this correct you are a true legend （＾-＾）
Describe what is meant by a malignant tumour (3 marks)
- Uncontrolled cell division
- Of unspecialised cells
- Cells break off and spread to other parts of the body
Describe and explain the appearance of a chromosome at the start of mitosis (2 marks)
- DNA replicated
- And condensed to be visible
Explain how the events that take place during interphase and mitosis lead to the production of two genetically identical cells (4 marks)
- DNA replicated in interphase
- Complementary base pairing
- Two sister chromatids are produced
- Each chromatid moves to opposite ends of the cell
Describe and explain how cell fractionation and ultracentrifugation can be used to isolate mitochondria from a suspension of animal cells (5 marks)
- Cell homogenisation to break open cells
- Filter to remove (large) debris / whole cells
- Use isotonic solution to prevent damage to organelles
- Keep cold to prevent damage by enzymes/ use buffer to prevent protein denaturation;
- Centrifuge at lower speed to separate heavy
organelles - Re-spin supernatant at higher speed to get mitochondria in pellet
Describe the function of the nucleus
- Contains genetic information
- Manufactures ribosomal RNA and ribosomes
- Acts as a control centre through the production of mRNA and tRNA for protein synthesis
Describe the function and structure of lysosomes
- Vesicle containing enzymes
- Breaks down cells
From production to secretion, list, in order, four organelles involved in making hormones
- Ribosomes
- Golgi Apparatus
- Golgi Vesicle
- Cell-surface membrane
Explain why toluidine blue stain is used whilst examining mitosis (2 marks)
- To make the chromosomes visible
- Since they contain the DNA of the cells
Contrast how an optical microscope and a transmission electron microscope work and contrast the limitations of their use when studying cells (6 marks)
6 of the following:
- TEM use electrons and optical use light
- TEM allows a greater resolution
- So greater detail in organelles/named cell structure can be observed
- TEM view only dead specimens and optical (can) view live specimens
- TEM does not show colour and optical
- TEM requires thinner specimens
- TEM requires a more complex preparation
- TEM focuses using magnets and optical uses
(glass) lenses
Describe how you would use cell fractionation techniques to obtain a sample of chloroplasts from leaf tissue without describing the solution (3 marks)
- Homogenise
- Centrifuge
- At different speeds until chloroplast fraction obtained
Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. Explain how (6 marks)
- Homologous chromosomes pair up
- Crossing over / chiasmata form
- Produces new combination of alleles
- Chromosomes separate
- At random
- Produces varying combinations of chromosomes / genes / alleles
- Chromatids separated at meiosis II / later
