Topic 1 - Cell Biology Flashcards
What are the 2 types of cell?
Eukaryotes and Prokayotes
all living things are made up of…
cells
Eukaryotes are…
complex. Animal and plant cells are eukaryotes
they are organisms that are made up of eukaryotic cells.
Prokaryotic cells are…
smaller and simpler e.g. bacteria. a prokaryote is a prokaryotic cell(single-celled organism)
what is the collective name for the different parts of a cell?
subcellular structures
subcellular structures of animal cells?
nucleus cytoplasm cell membrane mitochondria ribosomes
subcellular structures of plant cells?
everything an animal cell has
rigid cell wall
permanent vacuole
chloroplasts
Purpose of nucleus
contains genetic material that controls the activities of the cell
Purpose of cytoplasm
gel-like substance where most of the chemical reactions happen. it contains enzymes that control these chemical reactions.
Purpose of cell membrane
holds the cell together and controls what goes in and out
Purpose of mitochondria
these are where most of the chemical reactions for aerobic respiration take place. respiration transfers energy that the cell needs to work.
Purpose of ribosomes
these are where proteins are made in the cell
Purpose of rigid cell wall
made of cellulose. it supports the cell and strengthens it
Purpose of permanent vacuole
contains cell sap, a weak solution of sugar and salts
Purpose of chloroplasts
these are where photosynthesis occurs, which makes food for the plant. they contain a green substance called chlorophyll, which absorbs the light needed for photosynthesis
bacteria are…
prokaryotes
what subcellular structures do bacteria have?
cytoplasm
cell membrane
cell wall
what subcellular structures do bacteria not have?
chloroplasts
mitochondria
nucleus
what substitutes the nucleus in a bacteria cell?
they don’t have a “true” nucleus - instead they have a singular circular strand of DNA that floats freely in the cytoplasm
they also contain 1 or more small rings of DNA called plasmids
microscopes
they let us see things that we can’t see with the naked eye. the microscopy techniques we can use have developed over the years as technology and knowledge have improved
light microscopes
they use light and lenses to form an image of a specimen and magnify it. they let us see individual cells and large subcellular structures. like nuclei
electron microscopes
use electrons instead of light to form an image. have a much higher magnification than light microscopes. have a higher resolution (the ability to distinguish between 2 points, so a higher resolution gives a sharper image)
let us see much smaller things in more detail, like the internal structure of mitochondria and chloroplasts and even tinier like ribosomes and plasmids
what is the formula for magnification?
magnification= image size/real size
the image and real size have to have the same units
steps to prepare a slide for an onion:
- add drop of water to centre of clean slide
- cut up onion and separate layers. use teasers to peel off some epidermal tissue from bottom of 1 of the layers
- using tweezers place tissue in water on slide
- add drop of iodine solution, iodine solution is a stain. stains are used to highlight objects in a cell by adding colour to them.
- place cover slip on top. do this by standing it next to water droplet and slowly lowering it so it covers specimen. air bubbles obstruct view from specimen
how to record cells under a microscope?
fill up at least half the page
drawn in proportion
title for what is being observed and magnification
label important features (nucleus, chloroplasts)
differentiation
the process where a cell changes to become specialised for its job.
as cells change, they develop different sub-cellular structures and turn into different types of cells.this allows them to carry out specific functions.
when is differentiation lost?
most differentiation occurs as an organism develops.
in most animal cells, the ability to differentiate is then lost at an early stage, after they become specialised. however, lots of plant cells don’t ever lose this ability.
what are differentiated cells used for?
cells that differentiate in mature animals are mainly used for repairing and replacing cells, such as skin and blood cells.
what are undifferentiated cells called
stem cells
examples of specialised cells?
sperm cells - reproduction
nerve cells - rapid signalling
muscle cells - contraction
root hair cells - absorbing water and minerals
phloem and xylem cells - transporting substances
function of sperm cell
to get the male DNA to the female DNA. it has a long tail and a streamlined head to help it swim to the egg.
there are lots of mitochondria in the cell to provide the energy needed. it also carries enzymes in its head to digest through the egg cell membrane
function of nerve cell
to carry electrical signals from 1 part of the body to another. these cells are long (to cover more distance) and have branched connections at their ends to connect to other nerve cells and form a network throughout the body.
function of muscle cell
to contract quickly. they are long(to have space to contract) and contain lots of mitochondria to generate the energy needed for contraction.
function of root hair cell
they’re cells on the surface of plant roots, which grow into long “hairs” that stick out into the soil. gives the plant a bigger surface area for absorbing water and mineral ions from soil.
function of phloem cells
they form phloem tubes, which transport things such as food and water around plants. to form the tubes, the cells are long and joined end to end. they have very few sub-cellular structures, so that stuff can flow through them
function of xylem cells
they form xylem tubes, which transport things such as food and water around plants. to form the tubes, the cells are long and joined end to end. they are hollow in the centre
how does the nucleus store DNA?
the nucleus stores genetic material in the form of chromosomes
What are chromosomes
they are coiled lengths of DNA molecules. each chromosome carries a large number of genes. different genes control the development of different characteristics e.g. hair colour.
how many chromosomes do our cells have?
body cells normally have 2 copies of each chromosome - 1 from the organisms mother and 1 from its father. so humans have 2 copies of chromosome 1, 2, etc. 23 pairs of chromosomes for a human cell.
cells divide as part of?
body cells in multi cellular organisms divide to produce new cells as part of a series of stages called the cell cycle
what is mitosis?
the stage of the cell cycle when the cell divides. multi-cellular organisms use mitosis to grow or replace cells that have been damaged.
what does the end of the cell cycle result in?
2 new cells identical to the original cell, with the same number of chromosomes
what are the 2 main stages of the cell cycle?
growth and DNA replication
mitosis
steps of growth and DNA replication
- in a cell thats not dividing,the DNA is spread out in long strings
- before it divides, cell has to grow and increase amount of subcellular structures like mitochondria and ribosomes
- it then duplicates its DNA - so 1 copy for eah new cell. the DNAs copied and forms x-shaped chromosomes. each ‘arm’ of chromosome is exact duplicate of other.
steps of mitosis
after contents and DNA copied:
- chromosomes line up at centre of cell and cell fibres pull them apart. the 2 arms of each chromosome go to opposite ends of cell
- membranes form around each of the sets of chromosomes. these become the nuclei of the 2 new cells - nucleus has divided
- cytoplasm and cell membrane divide. cell has now produced 2 new daughter cells. these cells contain exactly the same DNA- identical to each other and parent cell
how do prokaryotic cells replicate?
by binary fission
binary fission
- circular DNA + plasmids replicate.
- cell gets bigger, circular DNA strands move to opposite ends of the cell
- cytoplasm begins to divide, new cell walls begin to form.
- cytoplasm divides, 2 daughter cells produced. each 1 has 1 copy of circular DNA, but can have a variable number of copies of plasmids
how do bacteria divide in different conditions?
divide quickly in right conditions (warm environment, lots of nutrients)
some bacteria like E coli only take 20 mins to replicate on right environment.
unfavourable conditions - cells can stop dividing, eventually begin to die
what is the mean division time?
the average amount of time it takes for 1 bacterial cell to divide into 2.
using mean division time to find number of bacteria in a population
make sure both times have same units
divide total time that the bacteria have been dividing by the mean division time, which gives the number of divisions
multiply 2 by itself for the number of divisions to find the number of cells
where are bacteria grown?
in a “culture medium” containing carbohydrates, minerals, proteins, and vitamins they need to grow.
it can be a nutrient broth solution or solid agar jelly
what will bacteria grown on agar plates do?
they will form visible colonies on the surface of the jelly, or will spread out to give an even covering of bacteria
how is an agar plate made?
hot agar jelly is poured into shallow round plastic dishes called petri dishes.
when cooled and set,inoculating loops(wire loops) can be used to transfer microorganisms to the culture medium. or a sterile pipette and spreader can be used to get an even covering of bacteria. microorganisms then multiply
what temperatures are used in school labs?
cultures of microorganisms are not kept above 25*C because harmful pathogens are more likely to grow above this temperature
what temperatures are used in industrial conditions?
cultures are incubated at higher then 25*c so that they can grow a lot faster
first step of the effect of antibiotics on bacterial growth
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
second step of the effect of antibiotics on bacterial growth
the antibiotic should diffuse(soak) into the agar jelly. antibiotic-resistant bacteria will continue to grow on the agar around the paper disks, but non-resistant strains will die. a clear zone will be left where the bacteria have died - this is called an inhibition zone
third step of the effect of antibiotics on bacterial growth
make sure you use a paper disk that has not been soaked in the antibiotic(control). instead, soak it in sterile water. you can then be sure that any difference between the growth of the bacteria around the control disk and a round 1 of the antibiotic disks is due to the effect of the antibiotic alone (and not something in the paper)
fourth and fifth steps of the effect of antibiotics on bacterial growth
- leave plate for 48 hours at 25*C
5. the more effective the antibiotic is against the bacteria, the larger the inhibition zone will be
steps of the effect of antibiotics on bacterial growth
- put penicillin in agar plate
- bacteria around the penicillin will die creating a clear zone
- use a control to check for errors
- leave it for 48 hours
- the more effective the penicillin the larger the clear zone
how to avoid contaminated cultures
petri dish and culture medium sterilised to kill unwanted microorganisms
inoculating loop sterilised by flame
lid taped on to prevent microorganisms from air
petri dish stored upside down to stop condensation dripping on agar surface
how to compare effectiveness of antibiotic ?
by looking at the relative size of the inhibition zones.
larger the zone the more effective the antibiotic against bacteria. find area
the area of a colony can also be measured the same way
what is differentiation?
the process by which a cell changes to become specialised for its job
what are undifferentiated cells?
stem cells, they can divide to produce lots more undifferentiated cells. they can differentiate into different types of cell depending on what instructions they’re given.
why are stem cells special and exciting?
embryonic stem cells have the potential to turn into any cell at all(all our cells had to come from them). when grown in a lab they can produce clones (genetically identical cells) and can be made to differentiate into specialised cells to use in medicine or research
where can stem cells be found
in adults it can be found in certain places like bone marrow but unlike embryonic stem cells (found in early human embryos,)they can’t turn into any cell at all just certain ones like blood cells.
how are adult stem cells used for medicine?
bone marrow can be taken to replace faulty blood cells in another person
how can embryonic stem cells be used to help others?
replace faulty cells - insulin producing cells can be made for people with diabetes, nerve cells for people paralysed by spine injury
how can an embryo be made to have the same genetic info as a patient?
therapeutic cloning, this means the stem cells produced also contain the same genes so wouldn’t be rejected by the patients body if used to replace faulty cells.
risks of using stem cells in medicine?
stem cells grown in labs may become contaminated with a virus that could be passed on to the patient to make them sicker.
why are some people against stem cell research?
they feel that the human embryo shouldn’t be used for experiments since each 1 is a potential human life
scientists should work more on finding and developing other sources of stem cells, so people could be helped without using embryos
in some countries is banned, allowed in UK under strict guidelines
what are the moral reasons for stem cell research?
curing existing patients who are suffering is more important than the rights of the embryos.
embryos used in research are unwanted ones from fertility clinics which if not used for research would be destroyed. (but they want fertility clinics banned too)
where are stem cells found in plants?
the meristem(where growth occurs). in a plants entire life cells in meristem tissue can differentiate into any type of plant cell
how can plants be cloned?
stem cells from meristem can be used to produce clones (identical copies) of whole plants quickly and cheaply.
why is plant cloning useful?
it can be used to grow more plants of rare species(to prevent extinction)
to grow crops of identical plants that have the desired features for farmers e.g. disease resistant
what is diffusion?
the gradual passive spreading out of particles from an area of higher concentration to an area of lower concentration
what substances can diffuse?
gases and solutions because they are free to move about randomly
what effects the time taken to diffuse?
the bigger the concentration gradient(difference in concentration) the faster the diffusion rate
higher temperature will give a faster diffusion rate because the particles will have more energy and will move around faster
why are cell membranes clever?
they hold the cell together but also let stuff in and out
dissolved substances can move in and out of cells by diffusion
what molecules can diffuse through cell membranes?
only very small molecules like oxygen, glucose, amino acids and water. starch and proteins cant fit
what affects the diffusion rate in cells
it is a random movement so some travel out but the majority go in because that is where the lower concentration is. the larger the surface the faster the rate of diffusion as more particles can pass through at once
what is osmosis?
the passive movement of water molecules across a partially permeable membrane from a region of higher water concentration to an area of lower concentration
what is a partially permeable membrane?
a membrane with very small holes in it. so small only tiny molecules like water can pass through. they pass both ways as water moves randomly but there is a steady net flow of water into the region with fewer water molecules
what happens with a strong sugar solution?
it’ll get more dilute, the water will try to even up the concentration on both sides of the membrane
first step of osmosis experiment
cut up potato into identical cylinders, get beakers with different solutions of sugar in them. 1 pure water, 1 very concentrated sugar solution and some inbetween
second step of osmosis experiment
measure mass of potato cylinders, then leave them in different beakers for about 24 hours
third step of osmosis experiment
take them out dry them and measure again
fourth step of osmosis experiment
if taken in water by osmosis - mass increase
if water drawn out - mass decrease
calculate percentage change , plot graph
fifth step of osmosis experiment
the dependant variable is the potato mass
independent is the concentration of sugar solution
what errors may occur?
if potato cylinders not fully dried, water gives a higher mass
water evaporates from beakers, concentration of sugar solutions change
repeat experiment and calculate mean percentage change to reduce effect of errors
what is active transport?
the movement of particles against a concentration gradient using energy
how are root hair cells adapted to be efficient?
each branch of a root will be covered in millions of tiny microscopic hairs which gives the plant a large surface area for absorbing water and mineral ions from the soil.
they need these for healthy growth
why cant root hair cells use diffusion?
the concentration of minerals is usually higher in the root hair cells then in the soil around them. minerals should move out of the root hair cells if they used diffusion.
how do root hair cells get minerals?
they use active transport
it allows the plant to absorb minerals from a very dilute solution, against a concentration gradient, its essential for growth. but it needs energy from respiration to work
does active transport happen in humans?
taking in glucose from the gut and from the kidney tubules
how do we use active transport in our gut?
when theres lower concentration of nutrients in gut, but higher in blood.concentration gradient is wrong way
so active transport used to allow nutrients to be taken into blood.
glucose can be taken into bloodstream when the concentration is already higher than the gut. can be transported to cells to be used for respiration.
what usually happens with nutrients in our gut
when there’s higher concentration of glucose and amino acids in gut they diffuse naturally in to our blood
what can diffusion in cells be used for?
to take in substances they need and get rid of waste products.
examples of what cells use diffusion for:
oxygen and carbon dioxide are transferred between cells and the environment during gas exchange.
in humans urea diffuses from cells into the blood plasma for removal from body by kidneys
what does the ability to diffuse easily depend on?
surface area to volume ratio
how does SA:V change the larger an organism is?
the larger an organism is the smaller its surface are to volume ratio is
what is diffusion like for single celled organisms?
in single celled organisms, gases and dissolved substances can diffuse directly in or out of the cell across the cell membrane. because they have a larger surface area to volume ratio so enough substances can be exchanged across the membrane to supply the volume of the cell
what is diffusion like for multi cellular organisms?
they have a smaller area to volume - not enough substances can diffuse from their outside surface to supply their entire volume. so they need an exchange surface for efficient diffusion.
what are exchange surfaces?
structures tat have to allow enough of the necessary substance to pass through
how are exchange surfaces adapted to maximise effectiveness?
thin membrane - substances only have short distance to diffuse
large surface area - so lots of substances can diffuse at once
in animals have lots of blood vessels - to get stuff in and out of blood quickly
gas exchange surfaces in animals ventilated - air moves in and out
What is the lungs job?
To transfer oxygen to the blood and to remove waste carbon dioxide from it. To do this the lungs contain millions of little air sacs called alveoli where gas exchange takes place.
How are alveoli specialised to maximise the diffusion of O2 and CO2?
An enormous surface area (about 74m squares in humans)
A moist lining for dissolving gases
Very thin walls
A good blood supply
What is the inside of the small intestine covered in?
Millions of these tiny little projections called villi.
What do villi do?
Increase the surface area in a big way so that digested food is absorbed much more quickly into the blood.
What do villi contain?
A single layer of surface cells
A very good blood supply to assist quick absorbtion.
What diffuses in a leaf?
Carbon dioxide diffuses into the air spaces within the leaf. Then it diffuses into the cells where photosynthesis happens. The leafs structure is adapted so that this can happen easily
How does carbon dioxide diffuse into a plant?
The underneath of the leaf is an exchange surface. It’s covered in little holes called stomata which the carbon dioxide diffuses in through.
What diffuses out of a plant?
Oxygen and water vapour diffuse out through the stomata. Water vapour is actually lost all over the leaf surface but mostly through stomata.
Water vapour evaporates from cells inside leaf. Then escapes by diffusion as there’s lots inside the leaf and less in the air outside
What controls the size of stomata?
Guard cells. They close the stomata if the plant is losing water faster than it is being replaced by the roots. Without them plant would wilt.
How does the structure of a leaf increase exchange surface area?
Flattened shape of leaf increases area of exchange surface so it’s more effective.
Walls of the cells inside the leaf form another exchange surface. Air spaces inside leaf increase area of this surface so there’s more chance for Co2 to get into cells
Where’s the gas exchange surface in a fish?
Gills are the gas exchange surface. Water containing oxygen enters the fish through its mouth and passes out through the gills. As this happens oxygen diffuses from water into blood int gills and CO2 diffuses from blood into water.
How are gills structured?
Each Gill is made of lots of thin plates called gill filaments, which give big surface area for exchange of gasses.
Gill filaments covered in tiny structures called lamellae which increase SA
What do lamellae have for diffusion ?
Lots of blood capillaries to speed up diffusion
Thin surface layer of cells to minimise the distance that the gases have to diffuse
Concentration gradients in fish gills?
Blood flows through the lamellae in 1 direction and water flows in other direction. This maintains a large concentration gradient between water and blood
Concentration of oxygen in blood?
Concentration of oxygen in water always higher than that in the blood so as much oxygen as possible diffuses from the water into the blood.
