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Biology - A Level > 2 - Cells > Flashcards

2 - Cells Flashcards

1
Q

Describe the function of the cell surface membrane:

A

allows for exchange of substances

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2
Q

Describe the structure of the nucleus:

A

-nuclear envelope (double membrane) with many pores
-nucleoplasm
-chromatin (diffused, uncondensed material that makes up chromosomes)
-nucleolus (may be more than one)

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3
Q

Give some functions of the nucleus:

A

-controlling the production of m/tRNA for protein synthesis
-holding genetic material in the form of linear DNA
-to manufacture ribosomal RNA and ribosomes in the nucleolus

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4
Q

Name the features of a mitochondrion:

A

-double membrane (inner membrane has folds known as cristae)
-viscous fluid inside is the matrix, and has the enzymes needed for respiration
-ribosomes

Can also have mitochondrial DNA

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5
Q

What are some features of chloroplasts?

A

-chloroplast envelope (double membrane)
-grana (stacks of thylakoid discs containing chlorophyll)
-stroma (fluid)
-starch grains
-ribosomes

Light-dependent reactions occur in thylakoids, independent in stroma

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6
Q

Give a feature of chloroplasts that allow proteins to be synthesised inside of them, and explain how it is different to the rest of the cell:

A

-they have DNA in them (similar to prokaryotic DNA, not associated with proteins and circular)

-they have 70S ribosomes, which are smaller than the 80S cytoplasmic ribosomes

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7
Q

Describe the structure of the Golgi apparatus:

A

-flattened sacs of single membranes called cisternae (similar to SER)
-Golgi vesicles forming by pinching off parts of the cisternae

cis face is closest to ER, trans is furthest (medial is inbetween)

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8
Q

Explain how molecules get used by the Golgi apparatus:

A

-incoming proteins/lipids are in vesicles from the ER
-modified and processed (eg adding carb. to make glycoprotein, glycosylation)
-molecules then leave in Golgi vesicles to be secreted

Molecules secreted could be enzymes like in the pancreas, or carbohydrates like in plants for cell walls

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9
Q

What is a lysosome?

A

a specialist form of a vesicle that contains hydrolytic enzymes to break down biological molecules

They are made when the vesicles from the GA contain enzymes

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10
Q

Give some of the main functions of lysosomes:

A

-to hydrolyse material ingested by phagocytic cells
-to secrete enzymes to the outside (exocytosis)
-digesting worn-out organelles to recycle their materials
-breaking down cells after death (autolysis)

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11
Q

Describe the structure of a ribosome:

A

-composed of a large sub-unit and a small sub-unit
-both contain rRNA and proteins

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12
Q

What is the endoplasmic reticulum?

A

-a system of flat sheet-like membranes (cisternae)

RER
-membranes are continuous with nuclear envelope and is covered in ribosomes

SER
-no ribosomes, and is involved in the synthesis/storage/processing of lipids/carbs/steroids

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13
Q

What is the structure of the cell wall?

A

-middle lamella that marks as a boundary between cell walls, cementing them together
-many polysaccharides including microfibrils of cellulose

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14
Q

How do cell walls differ between different types of organisms?

A

-in plants, it is made of cellulose
-in algae, it is made of cellulose or glycoproteins (or both)
-in fungi, it is made of chitin
-in bacteria, it is made of murein (aka peptidoglycan)

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15
Q

Describe the structure of a vacuole and how it contributes to its function:

A

-single membrane enclosing the cell sap is known as the tonoplast

-makes cells turgid for support by drawing water into the cell
-can act as a temporary food source (contains sugars + amino acids)

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16
Q

Why are arteries and veins considered organs, but not capillaries?

A

-arteries/veins contain multiple types of tissue
-capillaries only have epithelial tissue

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17
Q

How is the DNA different in prokaryotic cells?

A

prokaryotes have a single circular DNA molecule that is free to move about the cytoplasm (not inside a nucleus), and is not associated with proteins

The proteins specified are histones - a type of protein that allows for chromatin to be condensed and packed into chromosomes

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18
Q

Explain why a virus might only be able to infect one type of cell:

A

-the virus surface has attachment proteins
-its shape is complementary to the receptor proteins found on the cells
-only those types of cells will have the complementary receptor protein

19
Q

What is the formula for magnification?

A

image size/actual size

20
Q

Why is the solution buffered for storage before cell fractionation?

A

to stop large fluctuations in pH, which prevents the structure of organelles or enzymes from being altered

21
Q

How can you obtain a cell-free solution after homogenisation and filtration?

A

-centrifuge the sample at a low speed
-denser cells and cellular debris form a pellet at the bottom of the tube
-decant the supernatant into a separate tube

22
Q

Explain the principles behind how a TEM works:

A

-electrons pass through thin specimen
-denser parts absorb more electrons and will appear darker
-very short wavelength so higher resolution achieved

23
Q

Give some cons of using electron microscopes:

A

-specimen must be dead (either due to heavy metal stains, or because it is a very thin slice for TEMs, or because it is in a vacuum)
-can’t have true colour images
-lengthy sample preparation

24
Q

How are specimens measured under microscopes?

A

-eyepiece graticule is calibrated using a slide with a stage micrometer on it
-the length of each EPG unit is calculated using a ratio with the stage micrometer, so then specimens can be measured accurately

25
Q

Outline the roles of the different organelles in eukaryotes that are involved in protein formation/secretion:

A

-nucleus contains DNA which codes for proteins
-ribosomes on RER synthesise the protein
-mitochondria produce ATP to supply energy for this process
-Golgi apparatus modifies and packages them into vesicles which transport them to the cell membrane
-vesicles fuse with cell membrane for exocytosis

26
Q

What occurs during interphase?

A

-DNA replication
-cell growth

27
Q

What happens to the centrioles in mitosis?

A

P - moves to opposite sides of the cell
M - spindle fibres released and attach to either the centromere or chromatid
A - fibres retract causing centromere to break (requires ATP)
T - fibres break down

28
Q

How does this image show the cell is in anaphase?

A

-chromosomes are in 2 groups at the poles of the spindle fibres

-V-shape indicates the sister chromatids have been pulled apart at the centromeres

Don’t say ends of cell, always say poles

29
Q

How do prokaryotes undergo binary fission?

A

-circular DNA and plasmids are replicated
-cytoplasm divides to produce 2 daughter cells

30
Q

RP2 - Why is HCl used before making a root tip squash?

A

it softens and loosens the tissues, making it easier to flatten

31
Q

RP2 - root tip method: “Push down hard on the cover slip, but do not push the cover slip sideways.”

Explain why this instruction was given:

A

-push down hard to squash tissue, making a thin layer of cells for light to pass through

-don’t push sideways to avoid cells rolling together, which might break the chromosomes

32
Q

Why is cholesterol contained in plasma membranes?

A

-restricts lateral movement of the other molecules in the membrane

-makes it less fluid at higher temperatures, preventing leakage of water and dissolved ions

Cholesterol is a lipoprotein - a combination of lipid and protein

33
Q

Red blood cells contain more cholesterol than ileum lining cells - explain why:

A

-RBCs free in blood, not supported by surrounding cells like in the ileum
-cholesterol helps to maintain their shape

34
Q

Describe the 2 classes of proteins found in the plasma membrane:

A

peripheral - on surface, used for mechanical support + receptors

integral - carrier/channels for transport across membrane

Can also be called extrinsic/intrinsic

35
Q

What are glycoproteins and glycolipids used for?

A

-can allow for cells to attach to each other
-acting as recognition sites

36
Q

Describe how the movement of substances is affected by the structure of the cell membrane:

A

-PL bilayer allows for diffusion of small, non-polar molecules, but not larger polar molecules
-carrier proteins allow for AT
-channel/carrier proteins allow for fac. diff. or cotransport

-SA and the number of these proteins determine how much movement occurs and its rate

37
Q

RP3 - How would you determine the potato cylinder’s water potential after doing the osmosis experiment with a dilution series?

A

-plot a graph of %mass change vs concentration
-draw line of best fit and see where it crosses x axis

-use conversion table to turn the concentration into a water potential

38
Q

Suggest why putting honey, which has a high sugar concentration, onto a cut would kill the bacteria in it:

A

-honey has a lower water potential than inside the bacteria
-water leaves bacteria across PPM by osmosis
-loss of water in bacteria means metabolic reactions stop occuring, killing the cell

39
Q

RP4 - How could you quantitatively measure the transparency of a beetroot pigment solution?

A

-calibrate colorimeter

-get solution into cuvette and put in colorimeter
-set colorimeter to green filter (opposite to red) and take %absorbance/transmission readings

Always use the colour opposite to the specimen’s colour, as it is the colour the specimen will absorb the most of, maximising the accuracy of the experiment

40
Q

What is an antigen?

A

a foreign protein that stimulates an immune response

41
Q

Explain why antibodies only bind to certain things:

A

the binding site of antibodies have a specific 3D tertiary structure that is only complementary to one type of antigen to form an antigen-antibody complex

you lost a mark because of that last point

42
Q

Why does the population not need to be 100% vaccinated against a disease to prevent the spread?

A

-as long as most of the population is vaccinated, more people are immune
-this means unvaccinated people are less likely to come into contact with infected people

43
Q

Give an example of where mAb’s are used in a medical treatment:

A

targeted delivery of drugs to specific cells (eg cancer cells)

44
Q

Why aren’t antibiotics used to treat viral infections?

A

antibiotics work by disrupting metabolic processes in bacteria, but viruses don’t have metabolism

Biology - A Level (3 decks)

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