B1 - cell level systems Flashcards
what’s the difference between eukaryotes and prokaryotes?
eukaryotes are made from complex cells called eukaryotic cells, prokaryotes are smaller and are made up of simpler cells called prokaryotic cells (both types of cells contain sub-cellular structures)
what structures are found within eukaryotic cells?
- nucleus (a + p)
- cytoplasm (a + p)
- mitochondria (a + p)
- ribosomes (a + p)
- cell membrane (a + p)
- cell wall (p)
- chloroplasts (p)
what does the nucleus do?
it contains DNA (genetic material) in the form of chromosomes that controls the cell’s activities
what does the cytoplasm do?
it’s a gel-like substance where most of the chemical reactions happen
what do the mitochondria do?
these are the site of cellular respiration and contain the enzymes needed for the reactions involved
what do the ribosomes do?
these are where proteins are made in the cell
what does the cell membrane do?
it holds the cell together and controls what goes in and out by providing a selective barrier; they also contain receptor molecules that are used for cell communication e.g. by hormones
what does the rigid cell wall do?
it’s made of cellulose and provides support for the cell
what do the chloroplasts do?
this is where photosynthesis occurs, they contain a green substance called chlorophyll
what structures are found within prokaryotic cells?
- chromosomal DNA
- plasmids
- cell membrane
what does the chromosomal DNA do?
it consists of one long circular chromosome which controls the cell’s activities and replication, it floats free in the cytoplasm (not in a nucleus)
what do the plasmids do?
these are small loops of extra DNA that aren’t part of the chromosome; plasmids contain genes for things like drug resistance, and can’t be passed between bacteria
what does the cell membrane do?
controls what goes in and out, the cell is also supported by a cell wall
how are microscopes used to study cells?
microscopes use lenses to magnify images; they also increase the resolution of an image, this means they increase the detail you can see
what is resolution?
resolution is how well a microscope distinguishes between two points that are close together
what are the different types of microscopes?
light microscopes and electron microscopes (TEM and SEM)
what do light microscopes do?
they were invented in the 1590s and allow us to see things like nuclei and chloroplasts
what do electron microscopes do?
they were invented in the 1930s and allow us to see much smaller things in more detail (like the internal structure of mitochondria)- this has allowed us to have a much greater understanding of sub-cellular structures; only electron microscopes will let us see things as tiny as plasmids or viruses
what is the resolution of the light microscope?
up to 2x10^-7m
how does the light microscope work?
by passing light through the sample
describe three advantages of the light microscope
- they are small and portable
- they’re cheap to buy and operate
- it’s simple to prepare samples
describe one disadvantage of the light microscope
- lower resolution and limited magnification (1500x)
what is the light microscope used for?
to observe living and dead specimens
what are the two types of electron microscope?
- transmission electron microscope (TEM)
- scanning electron microscope (SEM)
what is the resolution of the TEM?
up to 1x10^-10m
how does the TEM work?
by passing a beam of electrons through a very thin section (slice) of a sample; the beam focuses and produces an image
describe one advantage of the TEM
- allowed scientists to view detailed images
describe three disadvantages of the TEM
- its large and difficult to move
- expensive to buy and operate
- sections have to be very thin to be used (around 100nm)
what is the TEM used for?
viewing sub cellular structures like nuclei, mitochondria and chloroplasts
describe one advantage of the SEM
- they provide detailed 3D images
describe three disadvantages of the SEM
- it’s large and difficult to move
- it’s complicated to prepare a sample and the sample must be dead
- expensive to buy and operate
what is the SEM used for?
to see detailed 3D structures of cells
what are the main parts of the light microscope and what do they do?
- eyepiece lens: looked through to see the image and also magnifies the image
- objective lens: magnifies the image, usually there are three different objective lenses (e.g. x4, x10, x40)
- stage: supports the slide
- clip: holds the slide in place
- handle: to carry the microscope with
- lamp: shines light through the slide so the image can be seen more easily
- focusing knobs: move the stage up and down to bring the image into focus
how is a specimen prepared to be investigated using a light microscope?
- the specimen needs to be able to let light through it so it can be viewed clearly so if it’s a thick specimen, a thin slice needs to be taken out of it
- then take a clean slide and use a pipette to put one drop of water or mountant (a clear, gloopy liquid) in the middle of it (this will secure the specimen in place
- use tweezers to place the specimens the slide
- add a drop of stain needed- if the specimen is completely transparent or colourless, a drop of stain is added to make the specimen easier to see; different stains are used to highlight different structures or tissues
- place a cover slip at one end of the specimen, holding it at an angle with a mounted needle
- carefully lower the cover slip onto the slide; press it down gently with the needle so that no air bubbles are trapped under it
how is a specimen viewed using a light microscope?
- start by clipping the slide containing the specimen onto the stage
- select the lowest-powered objective lens
- use the coarse adjustment knob to move the stage up to just below the objective lens; then, looking down the eyepiece, move the stage downwards until the specimen is just about in focus
- then, still looking down the eyepiece, adjust the focus with the fine adjustment knob, until you get a clear image of the specimen
- if the specimen needs to be viewed with greater magnification, swap to a higher-powered objective lens and refocus
how is total magnification calculated?
total magnification = eyepiece lens magnification x objective lens magnification
or
magnification = image size/real size
what is DNA?
a biological polymer made from nucleotide monomers; the sequence contains all of the information needed to make an organism
what makes up a nucleotide?
- phosphate
- sugar
- base
what are the base pair rules?
Adenine + Thymine
Cytosine + Guanine
= corresponding/complementary bases
what are proteins?
- proteins are polymers made up of amino acids; the monomers of a protein are amino acids
- the number and order of amino acids determines the protein shape and function
- proteins control key cell functions
what are the two stages of protein synthesis?
transcription and translation
what are the steps of transcription?
- during transcription, the DNA unzips so that both strands are separated
- one DNA strand acts like a template
- complementary bases attach to the strand being copied
- this forms mRNA, there is no Thymine in mRNA so Uracil is used
- the mRNA detaches itself and the DNA zips itself back up
what are the differences between DNA and mRNA?
- DNA has deoxyribose sugar, mRNA has ribose sugar
- DNA bases A+T C+G, mRNA bases A+U C+G
- DNA is double stranded, mRNA is single stranded
what are the steps of translation?
- mRNA attaches to the ribosome in the cytoplasm; the ribosome ‘reads’ the base sequence of the mRNA, 3 bases at a time
- triplet codes for specific amino acids are brought to the ribosome by tRNA
- mRNA moves along one triplet, and a second amino acid, coded for by this triplet is brought to the ribosome; when two amino acids are brought close together, they will bind together (peptide bonds)
- this process continues, forming an amino acid chain; a long chain of amino acids will form a protein, they will fold into the specific shape of a protein so it can easily perform its function
what is an enzyme?
a protein which acts as a biological catalyst, this means they speed up reactions without being used up
how does the enzyme fit a substrate to form an enzyme-substrate complex?
the active site of the enzyme has a complementary shape to the substrate
what factors affect enzyme-controlled reactions?
- temperature
- pH
- enzyme and substrate concentration
what does denatured mean?
where the shape of the active site has changed meaning the substrate will no longer fit into the enzyme
what is meant by the term ‘optimum temperature’?
the best and maximum temperature that the enzymes will react at
what happens if the pH is above or below the enzymes optimum?
if the pH is above or below the enzymes optimum the shape of the enzymes active site changes; this means that the sub state does not fit into the active site and the rate of enzyme activity decreases/stops, this results in the enzymes becoming denatured
describe and explain the effect of increasing substrate concentration on the rate of reaction
- when you increase the substrate concentration, the rate of reaction will steadily increase
- when all of the active sites of the enzymes have collided successfully with the substrates and are occupied in enzyme-substrate complexes and this is why the rate of reaction stops increasing
- the remaining substrates have nothing else to react with, this is the point of saturation
- the limiting reactant is the enzymes
what is respiration?
a chemical process that occurs (in mitochondria) in every cell of a living organism to release energy (ATP) for living processes
what do living organisms need energy for?
- building large molecules from smaller ones
- growth
- keeping body temperature steady
- muscle contractions so animals can move
what makes up ATP?
- adenine
- ribose sugar
- three phosphate groups
what are the word and symbol equations for aerobic respiration?
glucose + oxygen -> carbon dioxide + water
C6H12O6 + O2 -> CO2 + H2O
how many ATP molecules can be made?
32
to observe respiration, hydrogen carbonate indicator can be used, what is the meaning of its different colours?
hydrogen carbonate indicator is pink, it turns yellow if CO2 is added and purple if CO2 is removed
what is the word equation for anaerobic respiration in animals?
glucose -> lactic acid
what is oxygen debt?
the build up of lactic acid during anaerobic respiration causes oxygen debt, we ‘repay’ the oxygen by breathing deeply for some time after exercise has finished, the oxygen can break down the lactic acid to carbon dioxide and water
what are the word and symbol equations for anaerobic respiration in plants and microorganisms?
glucose -> ethanol + carbon dioxide
C6H1206 -> 2C2H5OH +2CO2
what is anaerobic respiration in plants and microorganisms also referred to as?
fermentation
how many ATP molecules are made from anaerobic respiration?
2
(less efficient than aerobic)
what nutrients are good sources of energy?
- carbohydrates
- proteins
- fats (lipids)
what do animals store glucose as?
glycogen
what do plants store glucose as?
starch
why are lipids not polymers?
they aren’t connected as a chain
what are carbohydrates made up of?
simple sugars
what are lipids made up of?
fatty acids and glycerol
what do you use to test for sugars?
Benedict’s reagent
what do you use to test for starch?
iodine
what do you use to test for lipids?
ethanol (the emulsion test)
what do you use to test for proteins?
the biuret test
what is photosynthesis?
the process by which producers make food; carbon dioxide and water react to form glucose and oxygen
what are the word and symbol equations for photosynthesis?
water + carbon dioxide -> glucose +oxygen
6H20 + 6CO2 -> C6H12O6 + 6O2
is photosynthesis an endothermic or exothermic reaction?
photosynthesis is an endothermic reaction
is respiration an endothermic or exothermic reaction?
respiration is an exothermic reaction
what is the rate of photosynthesis affected by?
- light intensity
- concentration of CO2
- temperature
(any of these factors can become the limiting factor)
what can you do to investigate how each factor is affecting the rate of photosynthesis?
by using pondweed and measuring oxygen production
- the rate at which pondweed produces oxygen corresponds to the rate at which it’s photosynthesising; the faster the rate of oxygen production, the faster the rate of photosynthesis
how is the pondweed experiment carried out?
- set up the equipment
- the pondweed is then left to photosynthesise for a set amount of time and as it photosynthesises the oxygen released will collect in the capillary tube
- at the end of the experiment, the syringe is used to draw the gas bubble in the tube up alongside a ruler and the length of the gas bubble is measured
- this is proportional to the volume of O2 produced
- the experiment is then repeated to test a range of values for the factor being investigated e.g. a range of different temperatures
- variables other than the one being investigated should be kept the same e.g. the other limiting factors, the time the pondweed is left for
(the amount of oxygen collected is not the total amount produced by photosynthesis - some of it is used up in respiration)
what is the inverse square law?
light intensity is proportional to 1/distance squared
