Cell biology Flashcards
1
Q
what are eukaryotes and prokaryotes?
A
eukaryote - organisms made up of eukaryotic cells
prokaryote - is a prokaryotic cell, its a single celled organism
2
Q
what are the similarities and differences between animal and plant cells?
A
similarities
- nucleus contains genetic material
- cytoplasm where most of the chemical reactions happen, it contains enzymes that control these reactions
- cell membrane (holds the cell together) and controls what comes in and out of the cell
- mitochondria reactions for aerobic respiration take place, respiration transfers energy that the cell needs to work
- ribosome where the proteins are made
differences
- cell wall supports the cell and strengthens it
- permanent vacuole contains cell sap, a weak solution of sugar and salts
- chloroplasts where photosynthesis occurs, which makes food for the plant
3
Q
what is the cell wall made of?
A
cellulose
4
Q
what do chloroplasts contain?
A
a green substance called chlorophyll, which absorbs the light needed for photosynthesis
5
Q
what type of cells are bacteria cells?
A
prokaryotic cells and they are much smaller
6
Q
what do bacteria cells contain?
A
- cell membrane
- cytoplasm
- cell wall
- a singular stand of DNA (instead of a nucleus) that floats freely in the cytoplasm
- one or more small rings of DNA called plasmids
- they don’t have chloroplasts or mitochondria
7
Q
what does a microscope do?
A
they let us see things that we can’t see with the naked eye
8
Q
what is the difference between a light and electron microscope?
A
light
- use light and lenses to form an image of a specimen and magnify it
- lets us see individual cells and large su cellular structures e.g. nuclei
electron
- use electrons to form an image
- they have a higher magnification than light microscopes
- they also have a higher resolution
- they let us see much smaller things in more detail like the internal structure of mitochondria and chloroplasts
9
Q
what is resolution?
A
the ability to distinguish between two points (so a higher resolution gives a sharper image)
10
Q
what’s the formula for magnification?
A
magnification = image size/real size
11
Q
how do you convert micrometers m into millimetres?
A
divide by 1000
e.g. 5000µm/1000 = 5mm
12
Q
how do you prepare a microscope slide? (practical)
A
- add a drop of water to the middle of a clean slide
- cut up an onion and separate it out into layers
- use tweezers to peel off some epidermal tissue from one of the layers
- using the tweezers place the epidermal tissue into the water on the slide
- add a drop of iodine (which is a stain) to highlight the objects in the cells by adding colour to them
- place a cover slip on top by standing the cover slip upright on the slide, and carefully tilt and lower it onto the specimen
- try not to get any air bubble or they will obstruct your view of the specimen
13
Q
what should your drawings of your observations under the microscope be like?
A
- make sure you use a pencil with a sharp point
- should not include any colouring or shading
- make sure the drawing takes up at least half the space available and that it’s drawn in clear unbroken lines
- if u are drawing cells the subcelluar structures should be drawn in proportion
- include a title of what u were observing and write down the magnification it was observed under
- label rhe important features of your drawing e.g. nucleus, chloroplasts using straight uncrossed lines
14
Q
what is differentiation?
A
the process by which a cell changes to become specialized for its job
15
Q
what are undifferentiated cells called?
A
stem cells
16
Q
how are sperm cells specialized for reproduction?
A
- it has a long tail and a streamline head to help it swim to the egg
- lots of mitochondria in the cell to provide the energy needed
- carries enzymes in its head to digest through the egg cell membrane
17
Q
how are nerve cells specialized for rapid signalling?
A
- they are long to cover more distance
- branched connections at their ends to connect to other nerve cells and form a network throughout the body
18
Q
how are muscle cells specialized for contraction?
A
- they are long so they have space to contract
- contain lots of mitochondria to generate the energy needed for contraction
19
Q
how are hair root cells specialized for absorbing water and minerals?
A
- long shaped hairs give big surface area for absorbing mineral ions and water from the soil
- ## active transport
20
Q
how are phloem and xylem cells specialized for transporting substances?
A
- form phloem and xylem tubes which transport substances such as food and water around plants
- cells are long and joined end to end
- xylem cells are hollow and phylum cells have very few subcellular structures so stuff can flow through them
21
Q
where are chromosomes located?
A
in the nucleus
22
Q
what are chromosomes?
A
- coiled up lengths of DNA molecules
- each chromosome carries a large number of genes, each gene controls the development of different characteristics
- body cells normally have two copies of each chromosome one from the mother and father
23
Q
how many pairs of chromosomes do we have in a human cell?
A
23 pairs (46 in total)
24
Q
what are the steps of mitosis?
A
growth and DNA replication
- DNA is spread out into long strings
- the cell grows and increases the amount of subcellular structures
- it duplicates its DNA (so there’s two sets of chromosomes one for each new cell) , each arm of the chromosome is a duplicate of the other
Mitosis
- chromosomes line up at the centre of the cell and cell fibres pull them apart
- the two arms of each chromosome go to opposite ends of the cell
- membranes form around each sets of chromosomes, becoming the nuclei of the new cells
- the cytoplasm and cell membrane divide
the cells produces two new daughter cells genetically identical to each other
25
what are the steps for binary fission?
- the circular DNA and plasmids replicate
- the cell gets bigger and the circular strands move to opposite poles of the cell
- the cytoplasm divides and new cell walls begin to form
- cytoplasm divides and two new daughter cells are produced
- each daughter cell has one copy of the circular DNA but can have a variable number of copies of the plasmids
26
What conditions do bacteria need to divide quickly?
warm environment and lots of nutrients
27
What happens if conditions are unfavourable for bacteria?
if conditions are unfavourable, the cells stop dividing and eventually begin to die
28
what is the mean division time?
the average amount of time it takes for one bacteria cell to divide into two.
29
a bacterial cell has a mean division time of 30 minutes. How many cells will it have produced after 2.5 hours?
2.5 hours x 60 = 150 minutes
150 minutes/30 minutes = 5 divisions
2 to the power of 5 = 32 cells
(divide the total time by the mean division time and multiply 2 by itself for the number of divisions)
30
what is a culture medium?
- where bacteria are grown in which contains the carbohydrates, minerals, proteins and vitamins they need to grow
- this can be a nutrient broth solution or solid agar jelly
31
why are cultures of microorganisms not kept above 25 degrees?
because harmful pathogens are more likely to grow above this temperature
32
How can you investigate the effect of antibiotics on bacterial growth? (practical)
- place paper discs soaked in different types (or different concentrations) of antibiotics on an agar plate that has an even covering of bacteria
- leave some space between the discs
- the antibiotic should diffuse into the agar jelly
- antibiotic resistant bacteria will continue to grow on the agar around the paper discs
- non resistant strains will die, a clear area will be left when they die called the inhibition zone
- use a control, a paper disc soaked in sterile water so you can be sure that any difference between the growth of bacteria around the control disc and the antibiotic disc is due to the effect of the antibiotic alone
- leave the plate for 48 hours at 25 degrees
- the more effective the antibiotic is against the bacteria the bigger the inhibition zone
33
how can you avoid contamination from unwanted microorganisms in the practical?
- petri dishes must be sterilised by heating to a high temp before use to kill any unwanted microorganisms
- if an inoculating loop is used to transfer bacteria to the culture medium, it should be sterilised by passing it through a hot flame
- the lid of the petri dish should be lightly taped on to stop microorganism in the air getting in
- petri dish should be stored upside down to stop condensation
34
what are undifferentiated cells?
- undifferentiated cells, called stem cells, can divide to produce lots more undifferentiated cells
- they can differentiate into different types of cells, depending on what instructions they’re given
35
where are stem cells found?
- in early human embryos, they have the potential to turn into any type of cell
- adult stem cells are found only found in certain places like bone marrow, they can’t turn into any cell type, only certain ones, such as as blood cells
- both these stem cells can be grown in a lab to produce clones and made to differentiate into specialised cells used in medicine and research
36
how can stem cells cure diseases?
- stem cells transferred form the bone marrow of a healthy person cba replace faulty blood cells in the patient who receives them
- embryonic stem cells could be used to replace faulty cells in sick people, you can make insulin producing cells for people with diabetes, nerve cells for people paralysed by spinal injuries
- in therapeutic cloning an embryo could be made to have the same genetic information as a patient. this means the stem cells produced would contain the same genes and so wouldnt be rejected by the patients body if used to replace faulty cells
37
what are the risks of stem cells?
stem cells grown in a lab may become contaminated with a virus which could be passed onto the patient and make them sicker
38
why are some people against stem cells research?
- they feel human embryos shouldn’t be used for experiments since each one is a potential human life
- others think curing existing patients who are suffering is more important than the rights of embryos
- they argue embryos used in the research are unwanted ones from fertility clinics which if they weren’t used for research, would probably be destroyed
- in some countries stem cells transferred form research is banned, it’s allowed in the UK as long as it follows strict guidelines
39
how can stem cells produce identical plants?
- in plants stem cells are found in the meristems
- throughout the plants life cells in the meristem tissue can differentiate into any type of plant cell
- these stem cells can be used to produce clones of plants quickly and cheaply
- they can be used to grow more plants of a rare species to prevent them from being wiped out
- they can be used to grow crops of identical plants that have desired features for farmers e.g. disease resistant
40
what is diffusion?
the movement of particles from an area of higher concentration to an area of lower concentration
41
what does diffusion happen in?
solutions and gases
42
what gives a faster diffusion rate?
- the bigger the concentration gradient. the faster the rate
- a higher temperature, will give a faster rate
43
how do cell membranes use diffusion?
- dissolved substances can move in and out of cells by diffusion
- only very small molecules can diffuse through the cell membrane like oxygen, glucose, amino acids and water
- big molecules like starch and proteins can’t fit
- particles move through the membrane through an area of higher concentration to and area of lower concentration
- they only move randomly so they go both ways but if they there’s a lot more particles on one side theres a net movement from that side
- the larger the surface area of the membrane the faster the diffusion rate because more particles can pass though at once
44
what is osmosis?
the movement of water molecules across a semi permeable membrane from an area of higher concentration to an area of lower concentration
45
what is a semi permeable membrane?
- only tiny molecules like water can pass through it and bigger molecules e.g. sucrose can’t
- water molecules pass both ways because water molecules move avout randomly
- theres a steady net flow of water into the region with fewer water molecules e.g. into the stronger sugar solution meaning it gets more dilute
46
what are the steps to investigate how sugar solutions affect plant tissue? (Practical)
- cut up potato into identical cylinders and get some beakers with different sugar solutions in them
- one should be pure water and another should be a very concentrated sugar solution e.g. 1 mol/dm³ ( can have a few other with concentrations in between e.g. 0.2, 0.4, 0.6)
- measure the mass of the cylinders then leave one cylinder in each beaker for 24 hours
- take them out, dry them with a paper towel and measure their masses again
- if the cylinders have drawn in water by osmosis, they will have increased in mass, if water have been drawn out, they’ll have decreased in mass
- calculate the percentage change in mass and plot a graph
- the dependant variable is the chip mass and the independent variable is the concentration of the sugar solution, all other variables time, volume of solution must be kept the same or it won’t be a fair test
- (errors) if some cylinders were not fully dried, the excess water would give a higher mass or water evaporating
- you can reduce the effect by repeating the experiment and calculating a mean percentage change at each concentration
47
what is active transport?
the movement of particles from an area of lower concentration to an area of higher concentration using energy from respiration
48
how do hair root cells take in minerals and water?
- the hairs stick into the soil
- each branch of a root is covered with millions of hairs
- gives the plant a large surface area for absorbing water + mineral ions
- plants need these mineral ions for healthy growth
- the concentration of minerals is usually higher in the root hair cells than in the soil
49
how is active transport used in the gut?
- used when there’s a lower concentration of nutrients (glucose and amino acids) in the gut but a higher concentration of nutrients in the blood
- active transport allows nutrients to be taken into the blood even if the concentration gradient is the wrong way
- this means glucose can be taken into the bloodstream when its concentration in the blood is already higher than the guy. it can be transported to cells for respiration
50
what organisms exchange substances with their environment?
- oxygen and carbon dioxide are transferred between cells and the environment during gas exchange
- urea diffuse from cells into the blood plasma for removal from the body by the kidneys
- how easy it is for an organism to exchange substances with its environment depends on the organisms surface area to volume ratio (SA:V)
51
how are exchange surfaces adapted to maximise effectiveness?
- they have a thin membrane so substances only have a short distance to diffuse
- they have a large surface area so lots of a substance can diffuse at once
- exchange surfaces in animals have lots of blood vessels to get stuff into an out of the blood quickly
- gas exchange surfaces in animals are often ventilated
52
how are the alveoli specialised to maximise diffusion?
- an enormous surface area
- a moist lining for dissolving gases
- very thin walls
- a good blood supply
53
how do the villi produce a really big surface area?
- the inside of the small intestine is covered in millions of villi
- they increase the surface area in a big way so that digested food is absorbed much more quickly into the blood
- they have a single layer of surface cells
- and a very goof blood supply to assist quick absorption
54
how does the structure of the leaves let gases diffuse in an out of cells?
- water vapour evaporates from the cells inside the leaf, then it escapes by diffusion because there’s a lot of it inside the leaf and less in the air outside
- Carbon dioxide diffuses into the air spaces within the leaf, then it diffuses into the cells where photosynthesis happens
- the underneath of the leaf is the exchange surface, covered in stomata
- oxygen and water vapour also diffuse out through the stomata
- the size of the stomata is controlled by guard cells, they close the stomata of the plant is losing water faster than it is being replaced by the roots
- without these guard cells the plant would wilt
55
what increases the surface area of the leaf?
-the flattened shape of the leaf in the area of this exchange surface so that it’s more effective
- the air spaces inside the leaf increase the area of this surface so there’s more chance for carbon dioxide to get into the cells
56
how does gas exchange happen in the gills?
- gills are the gas exchange in fish
- water enters the fish through its mouth and passes out through the gills
- as this happens oxygen diffuses from the water into the blood in the gills and carbon dioxide diffuses from the blood into the water
- the concentration of oxygen in the water is always higher than that in the blood so oxygen diffuses from the water to the blood
57
how do gills have a large surface area for gas exchange?
- each gill is made of lots of thin plates called gill filaments which give a big surface area for exchange of gas
- the gill filaments are covered in lots of tiny structures called lamellae which increase the surface area even more
- the lamellae have lots of blood capillaries to speed up diffusion
- they also have a thin surface layer of cells to minimise the distance that the gases have to diffuse
- blood flows through the lamellae in one direction and water in the opposite. this maintains a large concentration gradient
