cell biology Flashcards
define a cell
the basic unit of all forms of life
differences between eukaryotic cells and prokaryotic cells
- prokaryotic cells are much smaller in comparison
- prokaryotic cells have genetic material that is not enclosed in a nucleus like eukaryotic cells - instead it is a single DNA loop and there may be one or more small rings of DNA called plasmids
- prokaryotic cells don’t have mitochondria but eukaryotic cells do
centimetre, millimetre, micrometre and nanometre conversions
1cm = 10mm
1mm = 1000micrometres
1micrometre = 1000nm
define a eukaryotic cell
a cell that contains its genetic material (i.e. DNA) enclosed in a nucleus
function of the nucleus
contains genetic material that controls the activities of the cell
function of the cytoplasm
gel-like solution where most of the chemical reactions happen - contains enzymes that control these chemical reactions
function of the cell membrane
holds the cell together and controls what enters and leaves the cell
function of the mitochondria
where aerobic respiration takes place to release energy for the cell’s reactions
function of the ribosomes
sites of protein synthesis
animal cell sub-cellular structures
nucleus, cytoplasm, cell membrane, mitochondria, ribosomes
additional plant cell sub-cellular structures
CCV - chloroplasts, cell wall, vacuole
what cells have a cell wall and why
plant and algal cells have a cell wall made of cellulose, which supports and strengthens the cell
function of permanent vacuole
contains cell sap which helps keep the plant turgid and rigid
function of chloroplasts
organelles that contain chlorophyll to absorb light energy needed for photosynthesis - hence this is where photosynthesis takes place
define differentiation
a cell acquiring different sub-cellular structures to enable it to carry out a certain function - it has become a specialised cell
function of a sperm cell
to fertilise an egg
adaptations of a sperm cell
- they contain only half the genetic material of a normal adult cell, meaning that, when fertilisation takes place, they produce a normal body cell
- they have a long tail which allows them to swim to the egg and fertilise it
- they have an acrosome which contains enzymes that allow it to digest through the outer layer and cell membrane of the egg and fertilise it
- they have many mitochondria which provide energy for it to swim via aerobic respiration
function of a nerve cell
to carry electrical impulses around the body
adaptations of a nerve cell
- long axon; allows it to carry impulses over long distances
- myelin covered axons; insulate the axon which speeds up transmission of nerve impulses
- synapses; allow it to connect to other nerve cells and carry the impulse from one cell to another
- dendrites; increase surface area so other nerve cells can connect to it
function of a muscle cell
to contract and relax to allow for movement
adaptations of muscle cells
- they contain lots of mitochondria to release energy for muscular contraction using aerobic respiration
- they have protein fibres that can change their length, allowing the cell to contract and shorten
- they are long so that they have space to contract
function of a root hair cell
to absorb nutrients and water from the soil
adaptations of a root hair cell
- root hairs; increase the surface area of the root hair cells, allowing more water and mineral ions to be absorbed into the cell more effectively and more quickly
- lots of mitochondria; provide energy for active transport of mineral ions via cellular respiration
- large permanent vacuole; increased solute concentration inside the cell, ensuring a steep concentration gradient for water to diffuse across by osmosis
function of xylem cells
to carry water and dissolved mineral ions from the roots to the leaves
adaptations of xylem cells
- they have very thick walls containing lignin, a chemical that strengthens the cell, which helps to support the plant and allows it to withstand the high water pressure travelling through it
- there are no end walls between cells, meaning that the xylem cells form hollow tubes with open ends, allowing for a continuous flow of water and dissolved mineral ions to travel through these cells
– they have no nucleus, cytoplasm, vacuole or chloroplasts, allowing for more space for dissolved mineral ions and water to flow
function of phloem cells
to carry dissolved sugars ( the products of photosynthesis - glucose, sugar, amino acids) up and down the plant
adaptations of phloem cells
- little subcellular structures; allows glucose to travel through
- lots of mitochondria; provides energy for the active transport and translocation of sugars up and down the plant by respiration
- sieve plates rather than completely closed ends; allows dissolved sugars to travel from cell to cell, forming a tube
what are phloem cells made up of
vessel cells and companion cells
name organelles in bacterial cells
cytoplasm, cell membrane, cell wall, spherical nucleoid, plasmids
what is the difference between the nucleus of a bacterial cell compared to other cells?
bacterial cells don’t have a central nucleus that the genetic material is stored in. it has a spherical nucleoid in which all the DNA is held
what’s in a plant cell that isn’t in an animal cell
CVC - cell wall, (permanent) vacuole, chloroplasts
name organelles in animal cells
nucleus, cytoplasm, cell membrane, mitochondria, ribosomes
what are sperm cells specialised for
reproduction
what are nerve cells specialised for
rapid signalling
what are muscle cells specialised for
contraction
what are root hair cells specialised for
absorbing water and minerals
what are phloem cells specialised for
transporting substances
how does differentiation occur in animals and in plants
ANIMALS - most types of animal cell differentiate at an early stage; the ability to differentiate is normally lost at an early stage after they become specialised
PLANTS - many types of plant cell retain the ability to differentiate throughout life
what order were the microscopes invented
light microscopes first, electron microscopes second
how do light microscopes work
they use light and lenses to form an image of a specimen and magnify it
how do electron microscopes work
they use electrons to form an image
evaluate the use of light microscopes and electron microscopes
- an electron microscope has much higher magnification and resolving power than a light microscope - this means that it can be used to study cells in much finer detail
- light microscopes allow us to see individual cells and large sub cellular structures e.g. nuclei, whereas electron microscopes can only view dead and dry material
- light microscopes are typically cheaper than electron microscopes
- electron microscopes are large and static whereas light microscopes are smaller and portable
why did the invention of electron microscopes help develop microscopy
because electron microscopes allow us to see in a higher magnification and resolution, we can now see smaller sub cellular structures in finer detail and their internal structures can be investigated now as well due to the development of technology and scientific research
how do bacteria multiply, how often and under what conditions
via binary fission as often as once every 20 minutes, as long as they have enough nutrients and a suitable temperature
what culture mediums can bacteria be grown in
a nutrient broth solution or as colonies on an agar gel plate
what are uncontaminated cultures of microorganisms required for
investigating the action of disinfectants and antibiotics
how do you calculate the number of bacteria in a population after a certain time if given the mean division time
2 to the power of the amount of divisions
why must you sterilise Petri dishes and culture medium and how
using UV or an incubator, you should sterilise Petri dishes and culture medium to kill any unwanted microorganisms and prevent contamination
why must you sterilise inoculating loops and how
pass it through a flame, the flame kills any unwanted microorganisms and prevents contamination
what is the inoculating loop used for
transferring microorganisms to the media
why must the lid of the Petri dish be secured with adhesive tape
to prevent the lid falling off and unwanted microbes entering
why must the Petri dish be stored upside down into an incubator
to prevent condensation and moisture dripping down onto the bacteria and disrupting colonies
why must cultures generally be incubated at 25ºC in school labs
to reduce the chance of harmful bacteria growing - if we incubated it at higher temperatures, more dangerous microorganisms could grow
what does the nucleus of a cell contain
chromosomes made of DNA molecules; each chromosome carries a large number of genes
chromosomes come in
pairs (23 pairs in human body)
what is the cell cycle
body cells in multicellular organisms dividing to produce new cells
stages of the cell cycle
1) REPLICATION; the cell physically grows and replicates its sub-cellular structures (e.g. ribosomes, mitochondria) and the DNA duplicates to form two copies of each chromosome
2) MITOSIS; one set of chromosomes is pulled to each end of the cell and the nucleus divides
3) CYTOKINESIS; the cytoplasm and cell membrane divide to form two genetically identical daughter cells
why is cell division by mitosis important
- mitosis allows for growth and development of multicellular organisms
- mitosis allows multicellular organisms to grow or replace cells that have been damaged
define a stem cell
an undifferentiated cell of an organism which is capable of differentiating into any type of body cell
function of stem cells in embryos
cells in the early human embryo phase have not differentiated - at this point, the stem cells can be cloned and made to differentiate into most different types of human cells
function of stem cells in adult bone marrow
adult stem cells can differentiate into many types of blood cell (unlike embryonic that can differentiate into any type of cell)
function of stem cells in meristem tissue
meristem tissue in plants can differentiate into any type of plant cell throughout the life of the plant
what is therapeutic cloning
the process in which an embryo is produced with the same genes as the patient which reduces the likelihood of immune rejection because it is not a foreign antigen - therefore they may be used for medical treatment; once in the body, the embryonic stem cells could then differentiate and replace body cells that stopped working
benefits of stem cells
- therapeutic cloning reduces likelihood of immune rejection because the embryo is produced with the same genes as the patient
- it helps alleviate suffering of incurable diseases like diabetes and paralysis
risks of stem cells
- risk of transferring viral infections when transferring adult stem cells from donor to patient
- some people have ethical or religious objections to killing an embryo which had the potential for life and could not consent to doing so
- risk of immune rejection due to foreign object being inside body
two benefits of stem cells from meristems
- rare species can be cloned to protect them from extinction
- crop plants with special features such as disease resistance can be cloned to produce identical plants for farmers
how do substances move into and out of cells
across the cell membranes via diffusion
define diffusion
the spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration, down the concentration gradient
factors of affecting the rate of diffusion
- difference in concentrations; a large difference will lead to a higher rate of diffusion
- temperature; the higher the temperature, the higher the rate of diffusion. this is because increasing the temperature gives particles more kinetic energy so they are moving faster, hence will diffuse more quickly
- surface area of membrane; as surface area increases, the rate of diffusion also increases
explain how oxygen moves in and out of cells via diffusion
cells need oxygen for aerobic respiration carried out by mitochondria. cells are surrounded by a high concentration of oxygen because it is transported in the bloodstream from the lungs to the cells – this means that there is a high concentration of oxygen outside the cells and a low concentration of oxygen inside the cells, so oxygen diffuses from outside to inside the cell
explain how carbon dioxide moves in and out of cells via diffusion
as carbon dioxide is produced as a waste product of respiration, there is a high concentration of CO¬2 inside the cell and a low concentration outside the cell so the carbon dioxide diffuses out of the cell and into the blood
explain how urea moves in and out of cells via diffusion
urea is also a waste product produced inside cells, it diffuses out of the cells into the blood plasma and is excreted by the kidneys
relationship between the size of an organism and its SA:Vol ratio
the smaller an organism is, the larger the surface area to volume ratio
evaluate the use of stem cells from embryos or from adult bone marrow for treating human diseases
EMBRYOS:
pros;
- can treat a wide variety / lots of diseases / problems
- many available / plentiful
- painless
cons;
- (possible) harm / death to embryo
- (relatively) untested / unreliable / may not work
- embryo can’t be ‘asked’ / ’embryo rights’ idea
BONE MARROW:
pros;
- no ethical issues (in collection) or permission given
- quick recovery
- (relatively) safe well tried / tested / know they work
cons;
- they don’t treat as many diseases
- painful procedure
EVALUATION:
- embryos are better, because even though there are religious objections and concerns over not being able to consent, using them is better than wasting them
why does a unicellular not need any complex transport systems
a single-celled organism has a relatively large SA:Vol ratio; this allows sufficient transport of molecules into and out of the cell to meet the needs of the organism
why do large multi-cellular organisms like humans and plants need transport systems to exchange substances with their environment
to meet the needs of the organism, because, due to their sheer size, they have a very small SA:Vol ratio
why do we have organ systems
due to large multi-cellular organisms e.g. humans and plants having a very small SA:Vol ratio, cells in the centre of the organism are too far away from the surface to get enough oxygen and other substances needed for life - hence we have organ systems like the respiratory system and the circulatory system which has a very large surface area to allow us to get all the oxygen we need around our body
why do multicellular organisms have exchange surfaces in organ systems
to compensate for the low SA:V ratio
how is the small intestine adapted for exchanging substances with the environment
- villi increase the SA of the small intestine to increase the rate of diffusion of nutrients like glucose or amino acids
- villi have a rich blood supply of capillaries to remove nutrients quickly, in order to maintain a steep concentration gradient to increase rate of diffusion
- villi also have a very thin layer of cells (only one cell thick) to allow for a short diffusion path
- the small intestine is very long, giving substances a long time to diffuse, and also giving it a large surface area
how are the lungs in mammals adapted for exchanging substances with the environment
- the lungs are ventilated, which helps maintain the steep concentration gradient as new air is constantly being replaced, further increasing the rate of diffusion
- they have thin alveolar walls (only one cell thick) which allows for a short diffusion path of gases
- they have moist walls; gases dissolve in the moisture, which helps them to diffuse
- permeable walls to allow gases to diffuse through
- lungs are made up of tiny sacs called alveoli which present a very large surface area for gas exchange to take place
- lungs are well supplied with blood due to lots of capillaries covering the alveoli, constantly maintaining a large diffusion gradient
how are the gills in fish adapted for exchanging substances with the environment
- each gill is made up of lots of gill filaments which give a large surface area for the exchange of gases, increasing the rate of diffusion – the lamellae on the gills increase the surface area even more
- lamellae on the filaments of the gills have lots of blood capillaries to increase the rate of diffusion by removing oxygen quickly to help maintain a steep concentration gradient
- they have a thin layer of surface cells to allow a short diffusion pathway
how are the roots in plants adapted for exchanging substances with the environment
- idk fill this in
how are the leaves in plants adapted for exchanging substances with the environment
- they have stomata that allow lots of carbon dioxide in and oxygen to diffuse out – maintaining a steep concentration gradient
- the air spaces increase the area of the exchange surface because the walls of the palisade cells are the site of gas diffusion
- leaves are also relatively thin to allow a short diffusion pathway for carbon dioxide to diffuse across
why are the surfaces and organ systems of multicellular organisms specialised for exchanging materials
to allow sufficient molecules to be transported into and out of cells for the organism’s needs
the effectiveness of an exchange surface is increased by:
- having a large surface area
- a membrane that is thin, to provide a short diffusion path
- (in animals) having an efficient blood supply
- (in animals, for gaseous change) being ventilated
define osmosis
osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
define active transport
the movement of substances from a more dilute solution to a more concentrated solution (against a concentration gradient). this requires energy from respiration
describe how active transport works in the roots of plants
it allows mineral ions to be absorbed into plant root hairs from very dilute solutions in the soil; this is important because plants require ions for healthy growth
describe how active transport works in the gut
it allows sugar molecules to be absorbed from lower concentrations in the small intestine into the blood which has a higher sugar concentration, allowing us to maximise our sugar intake so that digestion is more efficient; this is important as sugar molecules are used for cell respiration
differences between AT, osmosis and diffusion
DIFFUSION:
- movement of particles from an area of higher concentration to an area of lower concentration
- doesn’t require energy
OSMOSIS:
- movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration
- doesn’t require energy
ACTIVE TRANSPORT:
- movement of particles against a concentration gradient
- requires energy
diffusion + osmosis: passive processes that do not require energy, active transport does require energy
