Cells Flashcards Preview

AQA A-Level Biology > Cells > Flashcards

Flashcards in Cells Deck (31)
Loading flashcards...
1

What are methods of studying cells?

Microscopy
Cell fractionation

2

Define magnification and resolution.

Magnification - how many times bigger the image is when compared to the object

Resolution - the minimum distance apart that two objects have to be for them to be distinguished as separate objects.

3

What is the equation for magnification?

Magnification = image size/actual size

4

Describe the process of cell fractionation

The tissue is placed in a cold buffered solution of the same water potential
Cells are broken up by a homogeniser (blender) - this releases organelles from the cell
The homogenate (the resultant fluid) is filtered to remove debris
The filtrate is placed in the centrifuge and spun initially at slow speeds
The heaviest organelles, like nuclei, are forced to the bottom of the tube where they form a thin sediment or pellet
The fluid at the top of the tube, the supernatant, is transferred to another tube and spun faster
This is repeated until the organelles are all split up

5

Why does the tissue have to be in a cold buffered solution of the same water potential at the start?

Cold - to reduce enzyme activity that might break the organelles.
Buffered - so that the pH does not fluctuate and alter organelle structure or affect enzyme functionality
Is of the same water potential as the tissue - to prevent organelles from bursting or shrinking as a result of osmotic gain or loss of water

6

What are the different types of microscopes?

Light microscope
Electron microscope
• Transmitting electron microscope
• Scanning electron microscope

7

Light microscope vs electron microscope

Light microscope:
Cheap
Portable
Staining to provide contrast
Less magnification and resolution
Uses light passing up from the specimen
Focussed by objective and eyepiece lens
Light has a longer wavelength

Electron microscope:
Expensive
Very large
No colour
More magnification and resolution
Uses a beam of electrons
Focussed using electromagnets
Electrons have a shorter wavelength
Living specimens cannot be observed - specimens coated in metal and viewed in vacuum

8

Transmission electron microscope vs scanning electron microscope

TEM:
Beam of electrons pass through thin specimen
2D image of inner structure
Specimen must be very thin

SEM:
Beam of electrons scattered from surface of specimen
3D image of specimen surface
Less magnification and resolution than TEM

9

What is the difference between eukaryotic and prokaryotic cells?

A eukaryotic cell is a cell which contains membrane-bound organelles

A prokaryotic cell is a cell that does not contain membrane-bound organelles

Another difference is that most eukaryotic cells have a nucleus, whereas prokaryotic cells do not

10

What are the common organelles in eukaryotic cells and what is their function?

Nucleus - contain the genetic material
Mitochondria - release energy in the form of ATP; respiration
Ribosome - protein synthesis
Cell membrane - control what goes in and out of the cell
Smooth endoplasmic reticulum - production and transportation of lipids
Rough endoplasmic reticulum - production and transportation of proteins
Golgi apparatus and vesicles - modify and transport proteins
Lysosome - contains enzymes to break up organelle debris
Cell wall - provide strength, structure and support
Chloroplast - photosynthesis
Vacuole - stores water and provides support

11

What are the common organelles in prokaryotic cells and what is their function?

Genetic material - free floating circular DNA
Plasmids - small rings of DNA
Capsule - layer of slime
Cell wall - made of polypeptides and polysaccharides
Cell membrane - control what goes in and out of the cell
Mesosome - helps with respiration
Ribosomes - smaller than eukaryotic
Flagellum - locomotion

12

Cell cycle

G1 - first growth phase, cell grows, increases in size
S - synthesis phase, DNA replicated
G2 - second growth phase, organelles replicate, further growth of cell
M - mitosis, cytokinesis

G1, S and G2 are all part of interphase

13

Stages of mitosis

Prophase - chromosomes condense, nuclear membrane disintegrates, spindle fibres start to form
Metaphase - chromosomes line up across the equator of the cell and attach to the spindle fibres via their centromeres
Anaphase - spindle fibres contract, chromatids are pulled apart at their centromeres
Telophase - chromosomes start to unravel, nuclear membranes start to form

14

Mitotic index

Ratio of cells undergoing mitosis to total cells
Measure of rate at which cells are dividing
The number of cells at each stage of mitosis is proportional to the time spent in each phase

Mitotic index = number of cells in mitosis / number of cells

A high mitotic index can be used to diagnose cancer

15

Virus structure

Viruses are non-living particles
They have genetic material, a capsid and attachment proteins

16

Structure of cell membrane

Phospholipid bilayer
- Hydrophilic head on outside
- Hydrophobic tail on inside

Cholestrol
- Strengthen the membrane
- Prevent leakage of water and ions

Embedded proteins
- Channel proteins which are holes that are specific and can be controlled by chemicals/electrical signal
- Carrier proteins which change shape when a molecule binds to it

Glycoprotein
- Allows cells to recognise each other
- Receptors for neurotransmitters and hormones

Glycolipid
- Recognition site
- Help cells to attach to one another and form tissues

Fluid mosaic model
Fluid - phospholipids can move relative to one another
Mosaic - embedded proteins vary in shape and size

17

Membrane permeability required practical

Fresh rinsed beetroot in water in boiling tubes in water baths, use colourimeter to measure light absorption of pigmented water
Independent - temperature
Dependant - light transmission
Control - size of beetroot, volume of water

18

Diffusion

Net movement of molecules from a region of higher concentration to a region of lower concentration.

To increase rate of diffusion:
High temperature
Large surface area
Short diffusion pathway
Steep concentration gradient

19

Facilitated diffusion

Diffusion involving the presence of proteins to allow the passive movement of substances across plasma membranes.

20

Osmosis

Net movement of water from a region of higher water potential to a region of lower water potential through a partially permeable membrane.

Water potential is the potential energy of water relative to pure water and is denoted by psi, ψ.

21

Osmosis in plant and animal cells

Plant cells
If the cell gains too much water it will become turgid, its protoplast pushed against the cell wall.
If the cell loses too much water, the cell will become plasmolysed, the protoplast pulled away from the cell wall.

Animal cells
If the cell gains too much water it will swell and burst, its membrane broken into fragments and its content released.
If the cell loses too much water, it will shrivel and shrink - in a red blood cell the haemoglobin becomes more concentrated, giving a darker appearance.

22

Osmosis required practical

Dried potato weighed and put in glucose solutions for 24 hours, taken out and dried and weighed again
Independent - concentration of glucose solutions
Dependent - percentage change in mass
Control - volume of solution, temperature, time left for

23

Active transport

Movement of molecules from a region of low concentration to a region of high concentration using ATP and carrier proteins

24

Co-transport

Transport of one substance coupled with that of another across a plasma membrane in the same direction through the same carrier protein

Co-transport of glucose
Sodium ions actively transported out of cells into blood through the sodium-potassium pump
Maintains much higher concentration of sodium in lumen of intestine than in cells
Carrying a glucose or amino acid molecule, the sodium ions diffuse from the lumen into the cells through co-transport proteins
Glucose/amino acids enter blood plasma by facilitated diffusion

25

Forms of transport

Diffusion
-- Simple diffusion
----- Osmosis
-- Facilitated diffusion
Active transport
-- Co-transport
-- Endocytosis
----- Phagocytosis
-- Exocytosis

26

Cells and molecules of the immune system

Macrophages
Phagocyte that kills pathogens and own cells
Devours cell debris and release interleukins

Interleukins
Chemical that searches bloodstream for recruitments
Increase temperatures to kill viruses

T cells
Produced in bone marrow
Mature in the thymus gland
Helper T cells - stimulate T cells and B cells by releasing cytokines
Cytotoxic T cells - perform targeted attacks

B cells
Produced and mature in bone marrow
Manufactures antibodies

Antibodies
Helps phagocytes fight off pathogens
Specific to an antigen

Cytokines
Activates B cells

27

How is an antigen presented?

A phagocyte engulfs a pathogen
Pathogen trapped in phagosome
Lysosomes fuse with phagosome
Lysozymes digest pathogen
Antigens transported to cell membrane and presented
A specific helper T cell is activated

28

Cell-mediated response

Phagocyte engulfs pathogens and presents antigens
T cell is activated and starts to divide - cloning by mitosis
Differentiate into:
Helper T cell - stimulate T cells and B cells
Cytotoxic T cell - perform targeted attacks
Memory T cell - remembers antigen for next encounter

29

Humoral response

Phagocyte engulfs pathogens and presents antigens
B cell is activated
Helper T cell releases cytokines to stimulate B cell to divide - cloning by mitosis
Differentiate into:
Plasma cells - produce and secrete antibodies
Memory B cells - remembers antigen for next encounter

30

Antibodies

Sturucture:
Y shape
Made of 4 polypeptide chains
Held together by disulfide bonds
Outer chains are light chains, inner chains are heavy chains
Very top are antigen binding sites, top parts are variable regions, middle and bottom are constant region
Can bind to 2 antigens at once

How they help:
Agglutination - clump pathogens together, much easier for phagocytes to engulf
Neutralisation - binding onto antigens prevents infection of more cells and they act as markers to attract phagocytes

31

HIV

Human Immunodeficiency Virus Infection:
Attaches onto protein receptors of helper T cell
Capsid fuses with membrane
Reverse transcriptase turns RNA into DNA
Viral DNA enters nucleus
Cell produces more viruses

Acquired Immunodeficiency Syndrome symptoms:
Susceptible to secondary infections and cancer
Infections of the lungs, intestines, brain and eyes
Weight loss and diarrhoea
Secondary infections can lead to death but not the HIV itself

Antibiotics:
Ineffective against HIV
They work against murein cell walls which HIV doesn't have
Can't reach viruses when they're in a host cell

ELISA test:
Apply antigens to a slide
Wash to remove unattached antigens
Add patient's sample and wash
Add second antibody with enzyme attached
Add colourless substrate
If there is a colour change, the enzyme is present, giving a positive result