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Biology Paper 1 > Topic 2: Cells > Flashcards

Topic 2: Cells Flashcards

1
Q

What is a microscope?
What is the object?
What is the image?
What is the simplest microscope?

A

Instruments that produce a magnified image of an object

Object = material under a microscope
Image = the appearance of the object when viewed under a microscope

Simple convex lens can act as a magnifying glass but are more effective as pairs in a compound light microscope

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2
Q

What is magnification?

What is the equation?

A

How many times bigger the image is than the object

magnification = image size / object size

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3
Q

What is resolution?

A

Resolving power - the minimum distance apart that two objects can be in order for them to appear as separate items.
Greater resolution = greater clarity
Depends on the wavelength / form of radiation that the microscope uses

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4
Q

Give the maximum resolution and magnification of light and electron microscopes

A

Light (optical):
Resolution = 0.2um
Magnification = x1500

Electron:
Resolution = 0.1nm
Magnification = x500,000

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5
Q

Give some general facts around light microscopes (that compare with electron microscopes)

A
  • Uses light, with beams focussed by lenses
  • Resolution determined by light wavelength
  • Thin specimen
  • No vacuum needed
  • Virtual image produced in eye
  • Specimen stained with iodine
  • Low cost, portable, little training
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6
Q

Give some general facts around electron microscopes (that compare with light microscopes)

A
  • Uses electrons focussed by electromagnets
  • Resolution determined by electron wavelength
  • Very thin specimen (TEM) or 3D specimen (SEM)
  • Vacuum needed
  • Image produced on fluorescent screen
  • Specimen stained with lead nitrate / another heavy metal
  • High cost, not portable, lots of training needed
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7
Q

How does a Transmission Electron Microscope work?

A
  • A beam of electrons fired from an electron gun and focussed onto specimen by a condenser electromagnet
  • Beam passes through a thin section of the specimen
  • Denser parts absorb more electrons so appear darker. Other parts let electrons pass through so appear brighter
  • An image is produced on a fluorescent screen and can be photographed to give a photomicrograph
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8
Q

What are the limitations of a Transmission Electron Microscope?

A
  • Whole system must be in a vacuum (air particles absorb / deflect electrons) = can’t view living specimens
  • Specimen must be extremely thin (to let electrons pass through)
  • Specimens killed and chemically fixed in a time-consuming, complex process
  • Complex staining process is required and image is still not in colour
  • Only captures 2D images
  • Image may contain artefacts (things that result from how the specimen is prepared that isn’t part of the specimen)
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9
Q

How does a Scanning Electron Microscope work?

A
  • Directs a beam of electrons across the surface of the specimen
  • Beam is passed back and forth in a regular pattern
  • Electrons scattered by the specimen depending on the surface contours ( depressions are dark, extensions are light)
  • Computer analysis builds up a 3D image
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10
Q

What are the advantages of a Scanning Electron Microscope?

A
  • Produces 3D images
  • Specimens don’t need to be thin (electrons don’t penetrate the specimen)
  • Preparation technique is less complex than TEM = less chance of artefact
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11
Q

What are the limitations of a Scanning Electron Microscope?

A
  • Resolving power lower than TEM (20nm) but still 10x better than light microscopes
  • Whole system must be in a vacuum
  • Image may contain artefacts
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12
Q

What piece of equipment would you use to measure the length of cells under a microscope?

A
  • Eyepiece graticule - a glass disc placed on the eyepiece.
  • Has a scale, usually 10mm with 100 eyepiece graticule units (EPGUs).
  • Visible when looking down the eyepiece. Must be calibrated for each objective lens
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13
Q

How do you calibrate an eyepiece graticule?

A
  • Use a stage micrometer - a special microscope slide with a scale, usually with 10 um divisions.
  • Line up stage micrometer and eyepiece graticule scales looking down the eyepiece
  • Find how many EPGUs are equivalent to 1 micrometer unit. Do 10um / this.
  • For different objective lenses, divide by the difference in magnification
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14
Q

What is the process that obtains samples of isolated organelles?

A

Cell fractionation - the process by which cells are broken up and the different organelles they contain are separated out

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14
Q

What are the three stages of cell fractionation?

A
  • Tissue placed in a cold, isotonic, buffered solution
  • Homogenation
  • Ultracentrifugation
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15
Q

Why are tissues placed in a cold, isotonic, buffered solution at the start of cell fractionation?

A
  • Cold - reduce enzyme activity that might break down organelles
  • Isotonic - same water potential as the tissue, prevents organelles bursting / shrinking from osmotic gain / loss of water
  • Buffered - pH doesn’t fluctuate, pH change could alter organelle structure or affect enzymes functioning
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16
Q

What is homogenation?

A
  • Cells broken up by a homogeniser (blender)
  • Releases organelles from the cell
  • Resultant fluid (homogenate) is filtered to remove any complete cells and large debris
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17
Q

Describe ultracentrifugation

A
  • Process where fragments in the homogenate are separated in a machine called a centrifuge. Spins the tubes at a high speed to create a centrifugal force
  • Spun at a low speed first, heaviest organelles sink to bottom + form a pellet
  • Supernatant (fluid at top) removed + spun at a faster speed. Repeat this process
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18
Q

In reference to ultracentrifugation, give some organelles in order of weight, starting with the heaviest, and give their rough speeds in a centrifuge

A
  • Nuclei (1000 revolutions/min)
  • Chloroplasts
  • Mitochondria (3500 revolutions/min)
  • Lysosomes (16,500 revolutions/min)
  • Ribosomes (100,000 revolutions/min)
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19
Q

What is a eukaryotic cell?

What is a prokaryotic cell?

What is a virus?

A

Have a distinct nucleus and are membrane-bound, with membrane-bound organelles

Have no nucleus or membrane-bound organelles. Much smaller. Stores food reserves as glycogen granules + oil droplets.

Acellular, non-living particles. Smaller than bacteria (20-300nm). Can only multiply in host cells

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20
Q

Name the organelles in an animal cell

A
  • Cell surface membrane
  • Ribosomes
  • Cytoplasm
  • Mitochondria
  • Lysosomes
  • Golgi apparatus
  • Nucleus
  • Rough endoplasmic reticulum
  • Smooth endoplasmic reticulum
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21
Q

Name the organelles in a plant cell

A
  • Cell-surface membrane
  • Chloroplast
  • Smooth endoplasmic reticulum
  • Rough endoplasmic reticulum
  • Mitochondria
  • Nucleus
  • Golgi apparatus
  • Vacuole
  • Cytoplasm
  • Ribosomes
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22
Q

What are the functions of the nucleus?

A

Functions:
- Controls cell activity
- Contains genetic material as DNA + chromosomes
- Manufactures ribosomal RNA and ribosomes
- Site of DNA replication + transcription so controls protein synthesis

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23
Q

What is the structure of the nucleus?

A
  • Nuclear envelope - double membrane surrounds nucleus. Continuous with RER, often has ribosomes on surface. Controls entry/exit of materials to nucleus
  • Nuclear pores - allows passage of large molecules e.g mRNA out the nucleus
  • Nucleoplasm - granular, jelly-like material makes up the bulk of the nucleus
  • Chromosomes - consist of protein-bound, linear DNA
  • Nucleolus - small spherical region in nucleoplasm. Manufactures rRNA and assembles ribosomes
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24
Q

What are the functions of mitochondria?

A
  • Site of aerobic respiration
  • Site of ATP production
  • DNA to code for enzymes needed in respiration
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25
Q

Describe the structure of a mitochondrion

A
  • Has a double membrane - outer controls entry/exit of material. Inner folds to form extensions (cristae)
  • Cristae - extensions of inner membrane, provide large surface area for attachment of enzymes and other proteins involved in respiration
  • Matrix - makes up remainder of mitochondria, has proteins, lipids, ribosomes, DNA to allow mitochondria to control production of their own proteins. Also has enzymes for respiration
26
Q

What is the function and structure of a chloroplast?

A

Function: site of photosynthesis
Structure:
- Chloroplast envelope - highly selective double plasma membrane
- Stroma - fluid-filled matrix where 2nd stage photosynthesis occurs, has starch grains + all enzymes needed to make sugars for that stage
- Thylakoids - disc-like structures containing photosynthetic pigment chlorophyll
- Grana - stacks of up to 100 thylakoids, where 1st stage photosynthesis occurs. Granal membranes have large S.A for attachment of chlorophyll, electron carriers + enzymes
- Lamellae - tubular extensions of thylakoid membrane link with thylakoids in adjacent grana
- Contain DNA + ribosomes so they can manufacture proteins for photosynthesis

26
Q

What are the functions of the rough endoplasmic reticulum?

A
  • Folds + processes proteins made at ribosomes
  • Have a large surface area for synthesis of proteins + glycoproteins
  • Provides a pathway for transport of materials, especially proteins, through the cell
27
Q

What is the structure of the rough endoplasmic reticulum?

A
  • Membranes enclose a network of flattened tubes called cisternae
  • Continuous with the outer nuclear envelope
  • Has ribosomes attached to the outer surface
28
Q

What is the function and structure of the smooth endoplasmic reticulum?

A

Function:
Synthesises, stores + transports carbohydrates + lipids

Structure:
Membranes enclose a network of flattened tubes called cisternae. Have no ribosomes attached

29
Q

What are the functions of the golgi apparatus?

A
  • Add carbohydrates to proteins to form glycoproteins
  • Secrete carbohydrates
  • Produce secretory enzymes
  • Transport, modify + store lipids
  • Forms lysosomes
30
Q

What is the structure of the golgi apparatus / how does it work?

A
  • A more compact stack of membranes that make up cisternae
  • Golgi vesicles are regularly pinched off the ends
  • Golgi modifies proteins, labels them so they can be sent to the right destination and transports them out the cell in vesicles
  • Golgi vesicles (small, fluid-filled sacs) move substances through the cell, then fuse with the cell-surface membrane + release their contents to the outside
31
Q

What are the functions of lysosomes?

A
  • Hydrolyse materials ingested by phagocytic cells
  • Exocytosis - release enzymes to outside the cell to destroy material around it
  • Digest worn-out organelles to re-use chemicals
  • Autolysis - completely break down cells after death
32
Q

What is the structure of a lysosome?

A
  • Formed when golgi vesicles contain enzymes. Also contain lysozymes (enzymes that hydrolyse cell walls of certain bacteria)
  • Lysosomes isolate enzymes before releasing them either outside the cell or to a phagocytic vesicle within the cell
33
Q

What is the function and structure of a ribosome?

A

Function: site of protein synthesis
Structure:
- One large, one small subunit each with ribosomal RNA and protein
- Two types: 80S in eukaryotic cells, 25nm diameter and 70S in prokaryotic cells, mitochondria and chloroplasts, slightly smaller

34
Q

What are the functions of the plant cell wall?

A
  • Provides mechanical strength to stop the cell from bursting by the pressure of osmotic entry of water
  • Gives mechanical strength to the plant as a whole
  • Allows water to pass along it + contributes to the movement of water through the plant
35
Q

What is the structure of the plant cell wall?

A
  • Plant cells - consist of microfibrils of cellulose embedded in a matrix
  • Thin layer called the middle lamella that marks the boundary between adjacent walls + cements them together
  • In fungi, they are made from chitin (a nitrogen-containing polysaccharide)
36
Q

What are the functions and structure of the cell vacuole?

A

Functions:
- Supports herbaceous plants by making cells turgid
- Temporary food store of sugars + amino acids
- Pigments can colour petals to attract pollinating insects
- Involved in the isolation of unwanted chemicals inside the cell

Structure: fluid-filled sac bound by a single membrane called a tonoplast

37
Q

What are the functions and structure of the cell-surface membrane?

A

Functions:
- Regulates movement of substances in/out the cell
- Has receptor molecules, allows it to respond to chemicals e.g hormones

Structure:
- Made from mainly lipids + proteins
- Molecules embed within it + attach to the outside

38
Q

Describe the stages of protein and lipid breakdown within a cell

A
  • Protein-containing vesicle from the RER transfers substances to the golgi apparatus
  • Lysosome combines with the vesicle containing the particle to be broken down
  • Enzymes hydrolyse the particle
  • Soluble products are absorbed into the cytoplasm
  • Insoluble debris is egested out the cell-surface membrane
39
Q

Why does cell specialisation occur?
What is a drawback of this?

A

No one cell can provide the best conditions for all functions so cells are specialised for a particular role. They perform their function more efficiently so the whole organism is more efficient

Lose their ability to carry out other functions = dependent on other cells

40
Q

How do cells become specialised?

A
  • At first, all cells in an embryo are identical
  • As it matures, cells become specialised
  • All cells contain same genes, but only some are expressed in any one cell at any one time = different cells have different characteristics
41
Q

What is a cell?
What is a tissue? Give some examples

A

Cell - a membrane-bound structure containing biomolecules

Tissue - group of similar specialised cells working together to carry out a specific function e.g
- Epithelial tissues - line surfaces of organs, often have a protective / secretory function
- Xylem - used to transport water / mineral ions up a plant + give mechanical support

42
Q

What is an organ? Give some examples

A

Combination of tissues coordinated to perform a variety of functions although they have one predominant function e.g
- Stomach - muscle (churns food), epithelium (protection/secretion), connective tissue (hold together other tissues)
- Leaf - palisade mesophyll (photosynthesis), spongy mesophyll (gas diffusion), epidermis (protection), phloem (transport organic materials away), xylem

43
Q

What is an organ system? Give some examples

A

Organs work together as a single unit e.g
- Digestive system - digests food: salivary glands, oesophagus, stomach, pancreas, liver
- Respiratory system - breathing / gas exchange: trachea, bronchi, lungs
- Circulatory system - pumps + circulates blood: heart, arteries, veins
- Nervous system - transmits signals between brain + rest of body: brain, spinal cord

44
Q

Give the organelles in a prokaryotic cell with their functions

A
  • Slime capsule: protects from other cells, bacteria stick together, prevents drying
  • Cell wall - murein (glycoprotein), prevents cell bursting from osmotic pressure, excludes certain substances
  • DNA - single circular molecule, not associated with histoproteins, no introns, floats in cytoplasm
  • Flagellum - only flagellated bacteria, hair-like structure rotates to facilitate directional movement
  • Plasmid - extra circular DNA floating free, genes may aid survival of bacteria in adverse conditions
  • Ribosome - 70S, site of protein synthesis
  • Cytoplasm - jelly-like substance containing organelles
45
Q

Give the organelles in a virus with their functions

A
  • Matrix - layer of proteins immediately under outer envelope
  • Attachment proteins - proteins used by virus to identify + attach to host cells
  • Capsid - protein layer that encloses 2 single strands of RNA and some enzymes
  • Nucleic acids - contain genetic material needed to reproduce
  • Lipid envelope - not present in all viruses
  • Reverse transcriptase - enzyme that catalyses production of DNA from RNA
46
Q

What is mitosis?

A

Cell division resulting in 2 genetically identical daughter cells, except in the rare occasion of a mutation.

47
Q

What is mitosis important for?

A
  • Growth of organisms
  • Repair - when cells die it is important that their replacements are identical in structure and function
  • Reproduction - single-celled organisms divide by mitosis
48
Q

What are the 4 stages of mitosis?

A
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
49
Q

Describe the prophase stage in mitosis

A
  • Chromosomes shorten and thicken (first become visible)
  • Animal cells have 2 centrioles (organelles) that move to opposite poles of the cell
  • Spindle fibres develop from the centrioles + span the length of the cell, collectively called the spindle apparatus
  • Nucleolus disappears + nuclear envelope breaks down = chromosomes free in the cytoplasm
50
Q

Describe the metaphase stage of mitosis

A
  • Chromosomes are made from 2 chromatids (each an identical copy of parent DNA) joined by the centromere
  • Microtubules attach to the centromere from the poles of the cell and chromosomes are pulled along the spindle apparatus to line up at the equator of the cell
51
Q

Describe the anaphase stage of mitosis

A
  • Centromeres divide in 2
  • Spindle fibres pull individual chromatids apart to opposite poles and are now referred to as chromosomes
  • Energy is provided by mitochondria which gather around the spindle fibres
  • If cells are treated with chemicals that destroy spindle fibres, chromosomes remain at the equator
52
Q

Describe the telophase stage of mitosis

A
  • Chromosomes reach respective poles and become longer and thinner. Eventually disappear, leaving only widely-spread chromatin
  • Spindle fibres disintegrate, nuclear envelope + nucleolus re-form
  • Cytoplasm divides in a process called cytokinesis
53
Q

What is the structure of a chromosome?

A

A pair of sister chromatids joined by a centromere

54
Q

How do you calculate mitotic index?

A

Number of cells with condensed chromosomes / total number of cells

55
Q

What is binary fission?
Explain its process

A

Cell division in prokaryotes

  • Circular DNA molecule replicates, both copies attach to the cell membrane at opposite poles. Plasmids replicate
  • Cell membrane grows between DNA molecules + begins to pinch inwards
  • New cell wall forms between DNA molecules, cell divides. Each daughter cell has a single copy of circular DNA and a variable number of plasmids
56
Q

What is viral replication?
Explain its process

A

Viruses are non-living so can’t undergo cell division.

  • Attach to host cell with the attachment proteins on their surface
  • Inject nucleic acid into the host cell. Provides ‘instructions’ for the host cell’s metabolic processes to start producing viral components.
57
Q

What are the three stages of the cell cycle?

Which lasts the longest?

A
  • Interphase
  • Mitosis
  • Cytokinesis

Interphase

58
Q

What are the three stages of interphase?

A
  • G1 (Gap Phase 1) - period of cell growth before DNA is replicated
  • S (Synthesis) - period when DNA is replicated
  • G2 (Gap Phase 2) - period after DNA is replicated. Cell prepares for division
59
Q

What is cancer?

A

A group of diseases caused by damage to genes that regulate mitosis, resulting in a tumour (a mass of abnormal cells).
Tumours become cancerous when they change from benign to malignant

60
Q

Define:
- Benign
- Malignant
- Metastasis

A
  • Benign - grows slowly, more compact, contained to one place
  • Malignant - grows rapidly, less compact, spreads to other parts of the body
  • Metastasis - the development of secondary malignant growths at a distance from the primary site of cancer
61
Q

What does the treatment of cancer usually involve?

A

Killing cells by blocking parts of the cell cycle. Usually:
- prevents DNA from replicating
- inhibiting the metaphase stage of mitosis by interfering with spindle formation

62
Q

Why is the treatment of cancer problematic for the body?

A

Drugs also disrupt the cell cycle of healthy cells. Although they are more effective against rapidly dividing cells so affect cancer cells more.
Normal body cells that divide frequently e.g hair-producing cells are also vulnerable to damage = why people lose their hair on chemotherapy.

Biology Paper 1 (9 decks)

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