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AQA A Level Biology > 2-3 Structure + Division > Flashcards

2-3 Structure + Division Flashcards

1
Q

What is the resolution?

A

Clarity, is the furthest away an image can be while still remaining as two separate objects

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2
Q

What is the nucleus?

A
  • Contains hereditary material
  • Nuclear envelope: double membrane, the outer membrane is continuous with the ER, controls the entry and exit of material
  • Nuclear pores: allows the passage of large molecules out of the cell
  • Nucleoplasm
  • Chromosomes: protein-bound DNA
  • Nucleolus: makes ribosomal RNA, assembles ribosomes
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3
Q

What are ribosomes?

A
  • Two subunits
  • Contains RNA and protein
  • Site of protein synthesis
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4
Q

What is the SER?

A
  • Lacks ribosomes

- Synthesises, stores and transports lipids and carbohydrates

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5
Q

What is the RER?

A
  • Has ribosomes present on the outer surface of the membrane

- Large surface area for the synthesis of proteins

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6
Q

What is the Golgi apparatus?

A
  • Flattened sacs or cisternae
  • Vesicles bring material from the ER
  • Processes and packages material
  • Produces secretory enzymes
  • Transports, modifies and stores lipids
  • Forms lysosomes
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7
Q

What are the lysosomes?

A
  • Hydrolyses material ingested by phagocytes
  • Exocytosis destroys material
  • Digests worn out organelles
  • Autolysis
  • Contains lysozymes which hydrolyse cell walls
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8
Q

What are the mitochondria?

A
  • A double membrane which controls the entry and exit of material
  • Cristae: extensions of the inner membrane, large surface area for respiration
  • Matrix: contains all the substances needed for respiration
  • Creates ATP
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9
Q

What is the vacuole?

A
  • Fluid-filled sac
  • A single membrane called a tonoplast
  • Contains pigments to attract pollinating insects
  • Temporary food store
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10
Q

What are chloroplasts?

A
  • Chloroplast envelope: double membrane, controls the entry and exit of material
  • Grana: stacks of thylakoids
  • Thylakoids: contains chlorophyll, some have extensions between adjacent grana
  • Stroma: a fluid-filled matrix that possesses all the enzymes needed for photosynthesis
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11
Q

How are chloroplasts adapted for photosynthesis?

A
  • Granal membranes provide a large surface area
  • Fluid possesses all the enzymes needed for sugar production
  • Contain both DNA and ribosomes to manufacture the proteins needed for photosynthesis
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12
Q

What is the difference between ribosomes in eukaryotic and prokaryotic cells?

A

80S: eukaryotic
70S: prokaryotic, found in mitochondria and chloroplasts

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13
Q

What is the cell wall?

A
  • Found in all plant cells
  • Consists of microfibrils of cellulose
  • Middle lamella marks the boundary between cell walls
  • Stops the cell from bursting under osmotic pressure
  • Strengthens the plant cell
  • Allows the movement of water
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14
Q

What is a tissue?

A

A group of similar cells that perform a specific function

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15
Q

What is epithelial tissue?

A

It consists of sheets of cells
It lines the surface of organs
Most have a protectors or secretory function

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16
Q

What is xylem tissue?

A

Found in plants
Used to transport water and mineral ions through the plant
Gives mechanical support

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17
Q

What is an organ?

A

A structure composing of two or more tissues which undergo one major function

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18
Q

What is an organ system?

A

A group of organs working together to perform a particular function

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19
Q

What is connective tissue?

A

The supporting tissue of the body

It binds structures together to provide support and protection against damage/infection/heat loss

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20
Q

What are prokaryotic cells?

A

They have no nucleus

Instead they have a single circular DNA molecule that is free in the cytoplasm and not associated with proteins

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21
Q

What are the differences between prokaryotic and eukaryotic cells in terms of cell walls?

A

P: have rigid cell walls made of polysaccharide and protein
E: have rigid cell walls mostly made of cellulose and only found in plant cells

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22
Q

What are the differences between prokaryotic and eukaryotic cells in terms of flagella?

A

P: have simple flagella
E: may have complex extension of cytoplasm to form cilia for coordinated movement

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23
Q

What are the differences between prokaryotic and eukaryotic cells in terms of respiration?

A

P: bacteria have mesosomes and algae use cytoplasmic membranes
E: have mitochondria

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24
Q

What are the differences between prokaryotic and eukaryotic cells in terms of photosynthesis?

A

P: no chloroplasts, only bacterial chlorophyll associated with the cell surface membrane in some bacteria
E: plant and algae cells contain chloroplasts

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25
Q

What are the differences between prokaryotic and eukaryotic cells in terms of fixing nitrogen?

A

P: some have the ability to fix nitrogen
E: cannot fix nitrogen

26
Q

What are the differences between prokaryotic and eukaryotic cells in terms of a capsule?

A

P: many have an outer mucilaginous layer called a capsule
E: don’t have a capsule

27
Q

What is the structure of a bacterial cell?

A

Cell wall: made of murein
Capsule: outer mucilaginous layer, only found in some species

Cell surface membrane
Plasmid: small, circular pieces of DNA
Flagellum: can be more than one, for movement
Cytoplasm: contains enzymes and other soluble material
Ribosomes: 70S

28
Q

What is a virus?

A

Smallest structure that shows life- 20-300nm
Genetic material: DNA or RNA but not both, small number of genes

Can’t be treated with antibiotics because there are no metabolic processes for them to inhibit
Can only multiply inside a host cell

29
Q

What is the structure of viruses?

A

Lipid envelope
Attachment proteins

Matrix
Capsid
Genetic material (RNA)
Reverse transcriptase

30
Q

What is the difference between prokaryotic and eukaryotic cells in terms of nuclei?

A

P: no true nucleus, only an area where DNA is found
E: distinct nucleus with a nuclear envelope

31
Q

What is the difference between prokaryotic and eukaryotic cells in terms of DNA?

A

P: DNA is not associated with proteins, some DNA is in the form of circular strands called plasmids
E: DNA is associated with proteins called histones, there are no plasmids, and DNA is linear

32
Q

What is the role of the cell wall in bacterial cells?

A

Physical barrier which protects the cell against mechanical damage, certain substances and osmotic lysis

33
Q

What is the role of the capsule in bacterial cells?

A

Protects bacterium from other cells and helps to group bacteria to stick together for further protection

34
Q

What is the role of the cell-surface membrane in bacterial cells?

A

Controls the entry and exit of materials

35
Q

What is the role of circular DNA in bacterial cells?

A

Possesses the genetic information for the replication of bacterial cells

36
Q

What is the role of plasmids in bacterial cells?

A

Possesses genes that may aid the survival of bacteria in adverse conditions

37
Q

What are unit conversions below millimetres?

A

There are 1000 nm in an µm

There are 1000 µm in a millimetre

38
Q

What is magnification?

A

The degree to which the size of an image is bigger than the size of an object

39
Q

What is a compound light microscope?

A

Light passed through a specimen, image formed on human retina, focused by glass lenses
Max magnification is about 1000, 500X better than the human eye

Resolves objects separated by 0.2 micrometers
Needs very thin specimens
Can be stained to show colours
Is portable

40
Q

What is an electron microscope?

A

Electrons are absorbed or deflected by molecules in air so a near vacuum has to be created
Beam can be focused using electromagnets because electrons are negatively charged
Greater resolving power is due to the electron beam having a shorter wavelength than light

41
Q

What is a transmission electron microscope?

A

Consists of an electron gun, electrons pass through the specimen, beam is focused by magnetic lenses, image formed by fluorescent screen
Max magnification is millions

Resolves objects separated by 0.02 nanometers
Specimen must be extremely thin to allow electrons to penetrate
Complex staining process doesn’t create a coloured image
The high powered electron beam can destroy the specimen
Image may contain artefacts

42
Q

What is a scanning electron microscope?

A

Specimens don’t need to be thin as electrons don’t penetrate
Specimen is sprayed with a thin coating of metal, electron beam is scanned across the surface of the specimen, metal emits secondary electrons
Emitted electrons can be focused by magnetic lenses
Image formed on fluorescent screens
Resolving power of 20nm, 10X better than light microscope
Creates a 3D image that is created by a computer analysis of the scattered electrons

43
Q

What is a centrifuge?

A

It is a device that spins very fast in order to separate liquids by masses

44
Q

What is differential centrifugation?

A

It is the separation of the different organelles within the cell

45
Q

What is homogenation?

A

It is the process of blending cells

Homogenate is the resultant fluid

46
Q

What is the method for differential centrifugation?

A

Cut tissue in an ice-cold isotonic buffer (cold to stop enzyme activity, isotonic to stop osmosis, buffer to stop pH changes)
Grind tissue in a filter to break down cells
Filter to remove insoluble cells
Place in a centrifuge at different speeds to separate the components

47
Q

What are the vague speeds for separation in differential centrifugation?

A 
Low = nuclei
Faster = mitochondria and chloroplasts
Faster = ER, Golgi and other membrane fragments
Fastest = ribosomes
48
Q

What is interphase stage of mitosis?

A

Gap 1 = cell growth, normal function
DNA synthesis = DNA is copied
Gap 2 = additional growth, chromatids become replicated chromosomes, centriole replicates

49
Q

What is the prophase stage of mitosis?

A

Chromosomes condense and become visible as they stain more intensely
Nuclear envelope breaks up into small vesicles
Nucleolus forms part of several chromosomes
Centrioles separate and take positions on opposite poles of the cell
Single fibres form and radiate towards the centre of the cell

50
Q

What is metaphase in mitosis?

A

Shortest phase
Chromosomes line up in the middle of the cell
Spindle fibres connect to the centromere of each sister chromatid

51
Q

What is anaphase in mitosis?

A

Spindle fibres start to contract
Centromeres that join the sister chromatid split
Sister chromatids are pulled apart
Separated chromatids move to opposite poles of the cell
Centromeres move first

52
Q

What is telophase in mitosis?

A

Chromosomes each consisting of a chromatid uncoil
A nuclear envelope forms around the chromosomes at each pole of the cell
Spindle fibres break down and dissolve
Cytokinesis begins

53
Q

What is cytokinesis?

A

The division of the cytoplasm that creates two separate cells
Made by constriction from the edge of the cell
Process differs in plant and animals
Animal cytokinesis: cell membrane forms a cleavage furrow that eventually pinches the cell into two clearly equal parts, each part containing its own nucleus

54
Q

Does mitosis occur if the cell is damaged?

A

No

An uncontrollable process can lead to tumours or cancer

55
Q

What is binary fission?

A

Occurs in prokaryotic cells
The circular DNA and plasmids replicate
The cytoplasm then divides to produce two daughter cells
Each daughter cell has a single copy of the circular DNA and a variable number of copies of plasmids

56
Q

Do viruses undergo cell division?

A

They don’t

They inject nucleic acid into the host cell so that the host will replicate the virus particles

57
Q

What is a somatic cell?

A

A typical body cell with twice the number of chromosomes as the gamete

58
Q

What are the factors that regulate the cell cycle?

A

Before a cell divides, the DNA is checked to make sure it has replicated correctly
A gene mutation occurs if DNA doesn’t copy directly

Chemical signals tell a cell when to stop or start dividing
Neighbouring cells communicate with dividing cells to regulate growth
Cancer is a disease of the cell cycle, some of the body’s cells divide uncontrollably and tumours form
Cancer can be caused by smoking, radiation, pollution and other chemicals. It can also occur naturally

59
Q

How do you calculate the mitotic index?

A

Mitotic cells
—————– X 100
Total cells

60
Q

How do you calculate magnification?

A

size of image
————————- = magnification
size of real object

61
Q

Why is tissue placed in an ice-cold, isotonic buffer solution?

A

Ice-cold to prevent enzyme activity
Isotonic to prevent osmosis
Buffer to prevent pH changes

AQA A Level Biology (19 decks)

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