cell biology Flashcards
what is the difference between a eukaryote and a prokaryote?
eukaryotic cells: animal cells, plant cells, and fungi. contain their genetic material (DNA) enclosed in a nucleus. they also have a cell membrane and a cytoplasm. cell walls are in plants and fungi, but not in animals. chloroplasts (in plants), mitochondria and ribosomes.
prokaryotic cells: bacteria (single-celled organism). these are much smaller than eukaryotes. they have a cell membrane, a cytoplasm and a bacterial cell wall. ribosomes. no chloroplast/mitochondria.
describe a bacterial flagellum:
thread-like structure protruding from the bacteria. rotates, propels the bacteria along, so it can move around
describe where the genetic material is enclosed in bacterial cells:
- genetic material not in a nucleus
- either in one circular strand of DNA, containing the genes they need to survive/reproduce
- also referred to as the circular chromosome/nucleoid
- also has small rings of circular plasmids which provide extra genes (e.g. antibiotic resistance)
compare the size of a eukaryote to a prokaryote:
eukaryotes (5-100 micrometres) are much larger than prokaryotes (0.2-2 micrometres).
what is meant by ‘order of magnitude’?
1 order of magnitude = 10x.
- a pineapple is 10x larger than a lemon, so it’s one order of magnitude larger than a lemon.
what is the function of the nucleus?
to enclose genetic material of the cell, controls its activities
what is the function of the cytoplasm?
watery, gel-like solution where chemical reactions take place. contains many of the cell organelles.
what is the function of the cell membrane?
partially-permeable layer. controls the molecules that can enter and leave the cell.
what is the function of mitochondria?
where aerobic respiration takes place. produces most of the energy for the cell’s chemical reactions to take place.
what is the function of ribosomes?
the sites of protein synthesis - proteins are incredibly important in cells. they provide support and strength, and can act as enzymes, among many other roles.
what are the three plant cell structures that aren’t in animal cells?
- chloroplasts - contain chlorophyll, and are the sites of photosynthesis.
- rigid cell wall - made of a chemical called cellulose, which strengthens and supports the cell - provides structure to it
- permanent vacuole - full of a fluid called cell sap. because it’s packed with this fluid, it gives the cell shape and stores excess nutrients (e.g. water, sugar, amino acids)
what is a ‘specialised cell’?
a cell that has adaptations to help it carry out a particular function. when cells become specialised, it’s called ‘differentiation’.
how is a sperm cell adapted to its function?
- the job of a sperm cell is to deliver genetic information to and join with an ovum (fertilisation). the genetic information of the sperm and ovum combine.
- contains genetic info in nucleus, but only half the amount of a normal adult cell.
- has a long flagellum (tail) and is streamlined, making the swim to the ovum easier.
- packed full of mitochondria, providing the energy needed for swimming.
- contains many digestive enzymes, allowing it to penetrate the ovum much easier.
what are specialised cells?
- specific role in the body
- to fulfil that role, they have a specific shape/structure
- specific amounts of different organelles
define differentiation:
the process by which cells change to become specialised
how is a neurone adapted to its function?
- sends electrical impulses around the body.
- has a long axon, carrying electrical impulses from one area of the body to another.
- a myelin sheath insulates the axon and speeds up the transmission of electrical impulses.
- has long dendrites, increasing the surface area so that other neurones can connect more easily.
how is a muscle cell adapted to its function?
- responsible for all movements under voluntary control.
- can contract (get shorter), as they contain protein fibres, which can shorten for contraction.
- packed full of mitochondria to provide energy for muscle contraction.
- muscle cells work together to form muscle tissue.
how is a root hair cell adapted to its function?
- absorb water and nutrients from the soil through osmosis.
- covered in hairs, which increase its surface area, meaning it can absorb water and dissolved more quickly and effectively.
- do not contain chloroplasts, as they’re underground and can’t photosynthesise.
how is a xylem cell adapted to its function?
- transport water and nutrients from the roots to the stems and leaves (TRANSPIRATION)
- found in the plant stem, long tubes.
- very thick walls containing lignin. provides support to the plant, but also causes the xylem cells to die (but this allows free travel of water).
- end walls between the cells have broken down, allowing water to pass through.
- dead cells, no subcellular structures, making it easier for water and minerals to flow.
how is a phloem cell adapted to its function?
- moves food substances that the plant has produced by photosynthesis to where they are needed (TRANSLOCATION)
- made up of sieve tubes, which are specialised for transport of nutrients (e.g. sugars, amino acids) and lack nuclei
- made up of living cells (contrary to xylem tubes)
- companion cells contain lots of mitochondria to provide energy for the transport
describe cell differentiation in animals:
- happens during an organism’s development. they start as one cell (a zygote), which undergoes mitosis to split into many daughter cells, which form an embryo. once part of an embryo, cells continue to undergo mitosis, and also begin to differentiate into specialised cells.
- it’s rare for cell differentiation to occur in an adult animal. it only occurs when replacing cells and repairing tissues.
describe cell differentiation in plants, and what is an advantage of it?
many plant cells keep their ability to differentiate throughout their life, as their roots and buds contain meristem tissue. this is why plants are always able to create new tissue (e.g. if you cut off a part from the stem of a plant, it’ll re-grow).
- we could clone a rare plant to prevent it from going extinct, or we could produce cloned crop plants for farmers.
what are the advantages of light microscopes?
- small
- easy to use
- relatively cheap
what are the limitations of light microscopes?
- limited magnification (can’t view sub-nucleus structures)
- have limited resolution, as they rely on light (the image is blurred, and we can’t see fine details)
- can see individual cells, but not the sub-cellular structures
what are the pros and cons of electron microscopes?
pros:
- much smaller resolution, therefore capable of using much higher magnification
- can use to study sub-cellular structures
cons:
- very expensive
- big
- hard to use
what is binary fission?
the process by which prokaryotic organisms (e.g. bacteria), divide and reproduce
describe bacterial division (binary fission):
- bacteria multiply by simple cell division (one bacterial cell splits into two bacterial cells).
- also a type of reproduction (asexual)
- bacteria can carry out binary fission every 20 minutes, as long as they have enough nutrients and the surroundings are warm and moist
- bacteria can be grown in a nutrient broth solution, or as colonies on an agar gel plate.
what are the stages of binary fission?
- cell must grow
- all genetic material must replicate. the two large circular strands move to either side of the cell, but the plasmids are distributed randomly
- a new cell wall is then grown down the middle of the cell, which then allows the two halves to pull apart
what equation would you use to answer this question:
‘under ideal conditions, a type of bacterium divides every twenty minutes. calculate the number of bacteria present after three hours.’
number of bacteria = 2^n
e.g.
3 hours = 180 minutes
180/20 = 9
number of bacteria = 2^9 = 512
512 = 5.12 x 10^2
why do organisms (especially young organisms) need a continuous supply of new cells?
a continuous supply of new cells enables organisms to grow, develop (new cell types as we develop new tissues), and repair.
- good for young organisms for growth
- older organisms still have to replace skin cells, which fall off our bodies
describe the cycle of mitosis:
- cell grow in size, and increases the numbers of sub-cellular structures (mitochondria, ribosomes)
- DNA is replicated, so each cell will have a full set of DNA
- DNA is condensed into chromosomes (which are basically coiled up packages of genetic material). these chromosomes contain a large number of genes, and control the development of different characteristics (e.g. eye colour). humans have 23 pairs of chromosomes.
- Each chromosome is duplicated, but stays attached to the original chromosome, forming an x-shape. Each half is called an arm. Each arm has the same DNA.
- All 46 of the cell’s chromosomes line up at the centre of the cell, and fibres from either side of the cell attach to their respective halves of the chromosomes, and pull these halves to opposite sides of the cell (opposite poles). this breaks the chromosomes apart into 2 separate arms
- the cell membrane and cytoplasm pull apart, forming two daughter cells with the same DNA. all the cells are identical (the daughters and the parent)
what are the three stages of the cell cycle?
- growth
- DNA replication + mitosis
- cytokinesis
what are stem cells?
- able to divide by mitosis to form more cells
- able to differentiate into specialised cells
what is an embryonic stem cell?
egg and sperm fertilise each other to form a zygote. this undergoes mitosis to form an embryo, containing many stem cells, which can differentiate into any type of cell
what is an adult stem cell?
an undifferentiated cell that is found in adults. however, these can only differentiate into certain types of related cells, don’t form any new tissues, can only replace damaged cells
e.g. stem cells in bone marrow can only differentiate into different blood cells.
describe a bone marrow transplant:
- leukaemia is a cancer of the bone marrow
- the patient’s existing bone marrow is destroyed using radiation. the patient then receives a transplant of bone marrow from a donor. the stem cells in the bone marrow now divide and form new bone marrow. they also differentiate and form blood cells.
what are medical conditions caused by?
- faulty cells (cells that have been damaged in some way, or that don’t work properly)
- type 1 diabetes is caused by damage to the insulin producing pancreas cells
- paralysis is caused by damage to nerve cells
- sickle cell anaemia is caused by misshapen blood cells
what are problems with bone marrow transplants?
- the donor must be compatible with the patient, otherwise the white blood cells produced by the donated blood marrow can attack the patient’s body.
- there is a risk that viruses can be passed from the donor to the patient.
describe stem cells in meristem tissue:
meristem tissue in plants (in the tips of the roots and shoots) can differentiate into any type of plant cell, throughout the life of the plant.
describe the uses of meristem tissue:
- can produce clones of plants quickly and economically.
- rare species can be cloned to protect from extinction.
- crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers.
what is therapeutic cloning?
- extract embryonic stem cells from early embryos
- grow them in a lab
- stimulate them to differentiate into whichever type of specialised cell we want
- give them to the patient to replace their faulty cells
what are the advantages and disadvantages of therapeutic cloning?
- can be used for a whole range of conditions (e.g. diabetes, paralysis)
- some people have ethical/religious objections to this procedure. the embryos have potential for human life, so some object. however, the ones used are usually unwanted ones from fertility clinics that would otherwise be destroyed
- requires embryonic stem cells, which are of limited supply
- rejection. the embryo and patient have different genomes, so the patient’s immune system may reject the cells. can use immunosuppressants, but they don’t always work
what are the advantages and disadvantages of using adult stem cells?
pros:
- taken from patient, so won’t cause rejection, and not in limited supply
cons:
- only differentiate into certain blood cells (can treat sickle cell anaemia, but not paralysis or diabetes)
what are the two main risks of stem cell use in medicine?
- virus transmission. if the donor stem cells are infected with a virus, when transferred into the patient, they’ll transfer the virus and cause even more problems
- tumour development. as stem cells can divide so quickly, it could get out of control when implanted into the patient, so could develop into a tumour/cancer
describe diffusion:
the spreading out of particles resulting in a net movement from an area of high concentration to an area of low concentration (moving down the concentration gradient)
- happens in both gases and liquids, or through some materials (e.g. cell membranes)
- oxygen and carbon dioxide diffuse in and out of cells for gas exchange.
- the waste product urea moves out of cells and into the blood plasma for excretion in the kidney.
what affects the rate of diffusion?
- a greater concentration gradient means that diffusion will take place faster
- the higher the temperature, the greater the rate of diffusion (particles have more kinetic energy)
- a larger surface area means that diffusion can occur more quickly
why is surface area: volume ratio a problem for multi-cellular, large organisms?
- low surface area : volume ratio
- we can’t rely on diffusion
- we need specialised exchange surfaces (e.g. lungs, intestines), which effectively increase our surface area : volume ratio, by increasing our internal surface area
describe the change in diffusion distances as organisms get larger:
as organisms get larger, the distance that molecules would have to diffuse to get from the outside of their body to the inside of their body increases massively
- diffusion will be way slower for large organisms, so they can’t rely on this alone to absorb nutrients into their cells
- they must rely on transport systems, like the circulatory system, so molecules only have to diffuse a very short distance to enter cells
what is the key idea of surface area: volume ratios?
as organisms get larger, their surface area:volume ratio decreases
- their volume increases much faster than their surface area
describe the surface area: volume ratio in unicellular organisms:
- e.g. bacteria
- high surface area : volume ratio
- can rely on diffusion across their surface to exchange everything they need
describe osmosis (special case of diffusion) :
the net movement of water molecules across a partially permeable membrane, from a region of higher water concentration, to a region of lower water concentration
define water concentration:
the amount of water compared to other molecules (like sugars/salts. they’re called solutes) that are dissolved in that water
- for example, a lower concentration of solutes means a higher concentration of water and vice versa
- it’s not the volume of water, but the proportion of water:solutes that determines the concentration
what is the partially permeable membrane used in osmosis in living organisms?
the cell membrane
describe active transport:
moves substances across a cell membrane from a lower concentration to a higher concentration (against the concentration gradient). this requires energy from cellular respiration.
- active transport always takes place across a membrane (e.g. cell membrane)
- it also requires special proteins that sit in the membrane and transfer the molecules from one side to the other
what is ATP?
small molecules that take energy created from cellular respiration in the mitochondria to the parts of the cell that need it
how does active transport benefit plants?
allows mineral ions (e.g. magnesium, nitrate ions) and water to be absorbed into plant root hairs from very low concentrations in the soil to very high concentrations in the roots.
- they therefore use energy to power active transport to absorb these nutrients against their concentration gradient
- root hair cells therefore have lots of mitochondria to enable active transport
- the root hair cells have long, hair-like protrusions that stick into the soil, and have a large surface area for maximum efficiency active transport
how does active transport benefit humans?
allows sugar molecules to be absorbed from lower concentrations in the gut into the blood, which has a higher sugar concentration. sugar molecules are used for cell respiration.
what is a cell?
smallest unit of life that can replicate independently
describe the difference in the replication of cells between animals and plants, and bacteria:
animals and plants: for growing, replacing dead cells. they’re multicellular organisms
bacteria: asexual reproduction, as the cell is the whole organism, therefore it also produces a whole organism
what are the parts of a light microscope?
- base at bottom, arm coming at the back
- light source (either lamp/mirror), with a stage above, where we place the microscope slide
- on top is all the lenses (three objective lenses with different magnifications). eyepiece lens which we look through with a fixed magnification
- also have the coarse and fine focusing knobs on the side, which help get the image in focus
how do microscopes work? (assume the light source is a mirror)
- light from the room hits the mirror and is reflected upwards through the object
- these rays pass through one of the objective lenses, then through the eyepiece lens, then into the eye
- the lenses will spread out the light rays, so the image we see is far larger than the object
define magnification, and what is its equation?
how many times larger the image appears than the object
equation: magnification = image size/object size
define resolution:
the shortest distance between two points on an object that can still be distinguished as two separate entities
how do you convert between:
- nanometres
- micrometres
- millimetres
- metres
- kilometres
- to convert to a larger unit, divide by 1000
- to convert to a smaller unit, multiply by 1000
how do you convert from centimetres to millimetres or metres?
cm-mm = x10
cm-m = divide by 100
what are specialised exchange surfaces?
the parts of an organism over which they exchange substances with the environment
- in humans, the main ones are alveoli and villi
- in plants, the main ones are root hair cells and leaves
describe alveoli:
- exchange carbon dioxide and oxygen with the air
- found at the very ends of the bronchioles in the lungs
- 100s of millions, meaning a huge area to absorb the needed oxygen molecules
describe villi:
- found on inside lining of small intestine
- help us to absorb nutrients such as glucose and amino acids
- long, thin shape
what are the common features of specialised exchange surfaces?
- large surface area. lots of molecules can diffuse across at the same time, so the rate of diffusion is higher
- very thin surfaces. only a short diffusion distance, so diffusion can take place more quickly
- exchange surfaces are permeable to the substance they need to exchange. (allow substances to diffuse across, rather then blocking them)
what is special about specialised animal exchange surfaces?
- good blood supply (e.g. the internal medium), which helps to maintain a concentration gradient. e.g. in villi, as soon as glucose is absorbed into the blood, it’s taken away, and replaced with blood with little glucose
- good supply of the external medium (e.g. a good surrounding supply of air in the alveoli). this maintains a good concentration gradient, as the medium is constantly replaced, aiding diffusion
describe fish gills:
water is capable of holding only a low amount of oxygen, so fish need a different exchange system - gills
- water is taken in through the fish’s mouth, passes over the gills, then out under the operculum
- each gill filament has a network of blood capillaries, and as the water flows over them, oxygen and carbon dioxide is transferred between the two
- water that flows over the gills flows in the opposite direction to blood (counter current flow). the exchange of oxygen and carbon dioxide is therefore more efficient than if they were both flowing in the same direction
why are the gills in fish efficient?
- large gill surface area
- large surface area of blood capillaries in each gill filament (high concentration gradient remains)
- short diffusion distance, only one cell thick
- efficient ventilation of the gills with water, the counter current flow (high concentration gradient remains)
