B1 Flashcards
What is a prokaryotic cell
A cell that does not contain a nucleus (emg a bacteria cell). They are simple cells and are typically smaller than Eukaryotic cells
What is a Eukaryotic cell
A cell containing genetic material in a nucleus. These cells are often complex and relatively large (emg plant and animal cells)
What are organelles
An organelle is a small structure in a cell which has a specific function
What organelles can be found in animal cells and what are their functions?
Nucleus - the DNA is stored here and it controls the actions of the vell - DNA (genetic material) is stored in chromosones
Mitochondria - This is where the cells respire. Enzymes catalyse a reaction between oxygen and glucose - forming ATP.
Ribosomes - The sight of protein synthesis
Cytoplasm - Where all chemical reactions in the cell take place
Cell membrane - A sellective barrier - allows some molecules to pass in and out of the cell. Also contains receptors
What organelles can be found only in plant cells and there functions
(Ribosomes, Nucleus, Cell membrane Cytoplasm, Mitochondria)
Chloroplasts - The site of Photosynthesis
Vacuole - Provides cell support + contains cell sap (sugar and salt solution)
Cell wall - Provides structure and support for the cell. Made up of cellulose
What is bacteria?
They are the smallest living organisms.
They are unicellular and every cell carries out the seven life processes - movement reproduction sensitivity growth respiration excretion and nutrition
What organelles do bacteria cells have
(cytoplasm, cell wall, cell membrane ribosomes)
Free floating genetic material - Normally circular, one long strand of DNA called the bacterial chromosome (in the cytoplam)
Flagella - tail like structure which allows the cell to move through liquids
Pili - hair like structures which allow the cell to attach to structures. They can also transfer genetic material between bacteria
Slime capsule - outside of the cell wall. Protects bacteria from drying out and from poisonous substances. It also protects the bacteria from drying out.
Plasmid - Circular piece of DNA used to store extra genes. These genes are not normally needed in the bacteriums day to day oife but do help in times of stress
They have NO membrane bound organelles
What is a light microscope.
A microscope used to observe small structures in detail.
The microscope passes through an object placed on a slide onto a stage, and through the objective and eyepiece lens the object is magnified.
Name the parts of a light microscope and what they do.
Eyepiece lens - Magnifies the image produce by the objective lens so it can be seen by the human eye
Objective lens - Directly observes the object - focuses reflected light into the ocular / eyepiece lense
Stage - where the specimen is placed for observation
Slide - Holds the specimen in place (with the cover slip on top) and protects the specimen from dust and contact
Light - the light passes through the sample to create an image
Fine focus - to fine tune the focus on the specimen (ensure its clear)
Coarse focus - to bring the specimen closely to focus
How do you set up your light microscope / observe cells through a microscope?
Lower the stage to its lowest position
Select the objective lens with the lowest magnification
Place the cell (on the slide) onto the stage
Turn the coarse focus slowly until you see an image
Turn the focus knob slowly until you see an image in a clear focus
If you want to see in greater detail repeat these steps using a greater magnification on your objective lens.
Remember to make sure the light is always on during this
How do you calculate the total magnification
Eyepiece lens magnification × objective lens magnification = total magnification
How do you calculate the size of an image (not actual size)
Actual object size × magnification = size of image
Why do we need to stain cells?
To make them easier to observe as many cells are transparent (and colourless)
What are the three main stains used
Methylene blue - makes it easier to see the nucleus of an animal cell
Iodine - makes it easier to see a plant nuclei
crystal violet - stains bacteria cell walls
How do you apply a stain
Place the cells on a glass slide
Add one drop if the stain
Place the coverslip on top
Tap the coverslip gently with a pencil to remove air bubbles
What are membrane bound organelles
Cellular structures which are bound to a biological membrane (e.g nucleus or mitochondria)
What is an electron microscope
A microscope which uses electrons (rather than light) to produce an image
What is the smallest size you can see with a light microscope
2×10-7m
What is a TEM
Transmission electron microscope
Produces the MOST magnified image.
Black and white 2d image.
A beam of electrons passes through a VERY thin slice of the sample. The beam is then focused into an image.
What is an SEM
Scanning electron microscope
Produces a 3d image.
A beam of electrons are sent across the surface of a specimen. The reflected electrons are collected to produce an image
Advantages and disadvantages of using a light microscope
Cheap and easy to operate
Small and portable
Simple to prepare a sample
Natural colour of sample is seen (unless staining is needed)
Specimens can be living or dead
Resolution of up to 2×10^-7m
Advantages and disadvantages of using an electron microscope
False colour can be added
Resolution to 1×10^-10
Expensive to buy and operate
Large and difficult to move
Sample preparation is complex
Black and white images are produced
Specimens are dead
What is resolution
The ability to distinguish two points being separate
What is DNA
DNA is generic material made up of 46 chromosomes (found in the nucleus) (half from your mum half from your dad)
What does DNA do
It determines what you are like, small sections of DNA called genes determine characteristics like eye colour.
What is a polymer
A substance which has a molecular structure built up by a large number of units
(A chain of monomers)
What is a monomer
A small molecule that can bond to others to form a polymer
How is DNA arranged
It is a double helix shape made from two strands that have a sugar phosphate backbone.
These strands are joined together by hydrogen bonds formed through complimentary base pairing of:
Adenine to thymine
Cytosine to guanine
What is a nucleotide
An organic molecule made from a nitrogenous base, sugar and phosphate
Is DNA a polymer or monomer
It is a polymer made from a monomer (nucleotides)
What does the DNA nucleotide look like
It is made of one phosphate
Deoxyribose (sugar)
And a Nitrogenous base ( A T C or G)
When these nucleotides join they form DNA.
What does DNA stand for
Deoxyribonucleic Acid
What is transcription
‘Copying DNA’ - the process of making mRNA
What is translation
The process in which proteins are made
How is DNA copied (not transcription)
The double helix structure unwinds leaving to connected strands.
These strands then disconnect from each other
Free floating nucleotides in the nucleus line up on the template strand (one of the two strands)
They connect to the template strand through complimentary base pairing and when joined the sugar phosphate backbone of formed
We now have one extra double helix of DNA
(This process happens on both of the strands)
What is a template strand
The template for transcription to occur and mRNA to be made
Describe the process of transcription
In transcription a Gene is copied
The DNA unwinds and unzips at that gene.
Free floating RNA nucleotides join to the template strand through complimentary base pairing
The gene can then zip back up and wind up and we are left with an mRNA template strand
The mRNA is small enough to leave the nucleus (through its pores) and it travels to the nucleus.
What does a RNA nucleotide look like
Stands for Ribonucleic acid
Contains a phosphate
A sugar (ribose)
And 4 bases Adenine Uracil Cytosine and Guanine
(A to U) (C to G)
Describe and the process of translation
This process is protein synthesis.
The mRNA travels to and ‘sits’ on the ribosomes.
MRNA is read in codons (or triplets) which means groups of 3 bases are read at one time.
tRNA comes from the cytoplasm and is made from anticodons (the opposite bases to codons) and an amino acid.
The tRNA joins to the mRNA if the codons and anticodons ate complimentary.
This then causes the amino acids to form peptide bonds.
Eventually this string of amino acids will leave the ribosomes and become proteins (folding into complex 3D shapes)
How is the shape of protein determined
By the sequence of amino acids (which is determined by the mRNA and tRNA)
Every protein has its own specific shape
What are enzymes
All enzymes are made from protein and they work as biological catalysts.
They speed up reactions WITHOUT being used themselves
They lower the activation energy needed for the reaction to take place
What are the two main things enzymes do?
Build large molecules from smaller ones (anabolic)
Break down larger molecules into smaller ones (catabolic)
What is a substrate
The molecule that binds to an enzyme
How do enzymes and substrates bond
An enzyme substrate complex can be formed if the enzymes ACTIVE SITE is the same shape as the substrate and they can bind
Do enzymes bind to all molecules
No
They only bind to one type of substrate molecule which fits in its active site
Lock and key hypothesis - only one shaped key can fit in and open a lock
How do enzymes change the substrate.
If they are catabolic they break the bonds between the substrate
If they are anabolic they create bonds between the substrate
What are the 3 main factors that affect enzyme controlled reactions
Ph
Temperature
Enzyme / substate concentration
How does a temperature being too high affect an enzyme controlled reaction
The amino acid chains in the protein begin to unravel - changing the shape of the active site.
This means the enzyme is denatured and substrate cannot bind to the active site, so the rate of reaction decreases
Many denatured enzymes cannot be fixed
How do low temperatures effect enzyme controlled reactions
At a low temperature the enzymes and substrates have less kinetic energy.
This means less collisions between enzymes and substrates will occur
Therefore the rate of reaction will be slower.
How does pH affect enzyme controlled reactions
Each enzyme has an optimum pH
A change in pH affects the interactions between amino acids in a chain
This could make the enzyme unfold and change the shape of the active side (denature)
What is the optimum temperature for enzymes in a human
37°C
How do enzyme concentration and substrate concentration affect enzyme controlled reactions
Enzyme concentration - the more enzymes the more substrate that can bind to then (increases reaction until all substrate is used up / enzymes are full)
Substrate concentration - more substrate means that the rate of reaction will increase untill all enzymes are forming ESC’s so new substrate cant be used up
What is your metabolic rate
The rate at which your body transfers energy from chemical stores
What are carbohydrates
Polymers made from smaller molecules like sugars.
They provide energy and are the substrate used in resperation
They are broken down by enzymes called carbohydrase.
An example is starch which is broken down by amylase
What are proteins
All enzymes are protein
Protein is made from amino acids (protein is a polymer)
Protein is broken down by protease
Proteins are used for growth and repair
(Examples include insulin and hemoglobin)
What are lipids
Lipids ARE NOT POLYMERS
They are made from glycerol and fatty acids
They make up fats and oils
The also provide energy and can be substrates for respiration
Broken down into by lipases
What are food tests?
Experiments allowing us to see what food type a food contains
How do you test for starch (carbohydrates)
Place a small amount of iodine on the food. If it turns blue black starch is present
How do you test for sugars (Carbohydrates)
Use benedicts test
Add benedicts solution to the food (dissolved in water) and place it in a water bath
Reducing sugars will react with the solution and show a brick red colour (e.g glucose)
If no glucose is present the solution will be green
How do you test for lipids
Add ethanol to your food solution
Shake and then leave for a minute.
Pour the ethanol into water
If it turns cloudy lipids are present
How do you test for protein
Biuret test
Add a few drops of copper sulfate to your solution
Next add a few drops of sodium hydroxide.
If the solution turns purple proteins are present
What is aerobic respiration
Process of transferring energy from glucose and oxygen - the complete breakdown of glucose
Glucose + oxygen → carbon dioxide + water
It is an enzyme controlled reaction
It occurs in the mitochondria (the more mitochondria a cell has the more it respires the more active it is)
It is exothermic
Where is energy transferred to in aerobic respiration
It is transferred to an energy store called ATP
38 ATP is produced in aerobic respiration
What is ATP and its main functions in the body?
ATP is a chemical store
It stands for Adenosine TriPhosphate
It is made of Adenosine (a base) and 3 phosphate bonds
It is used to synthesise larger molecules from smaller ones - to make new cell material
It is used in movement
It is used to stay warm
What is anaerobic respiration
Process of transferring energy from glucose in absence of oxygen
Glucose → lactic acid (glucose is not fully broken down)
2 ATP molecules are made
This process occurs in the cytoplasm
In plants
Glucose → ethanol + carbon dioxide
What is oxygen debt
When we anaerobically respire we are releasing quick energy for a short amount of time
We need oxygen in order to break down lactic acid - so after we anaerobically respire we are in oxygen debt
How do plants respire anaerobically
Plants and fungi respire anaerobically and produce ethanol and carbon dioxide. This process is called fermentation.
Glucose → ethanol + carbon dioxide
This reaction transfers energy from glucose
We use fermentation to make alcohol
What is photosynthesis
Process by which producers make food - carbon dioxide + water → glucose + oxygen
Endothermic
Enzyme controlled reaction
Where does photosynthetis occur
It occurs in the leaves - specifically inside the chloroplasts
What are the two stages of photosynthesis
Light dependent - energy transferred from light splits water molecules into hydrogen and oxygen ions (hydrolosis)
Light independent - carbon dioxide gas combines with hydrogen ions to make glucose
What do plants use glucose for
Some are immediately used in respiration
Other glucose molecules are converted into other sugar molecules
Glucose that is not used right away is converted to starch
What are plants made of (other than sugars and starch)
Proteins, cellulose, fats from sugars and other substances
Photosynthesis experiments - testing for starch
Take your leaf and kill it by placing it in boiling water.
Wash the leaf with water to remove ethanol and to soften the leaf
Place it on a white tile and add drops of iodine.
If starch is present it will turn from brown to blue/black
Photosynthesis experiments - prove chlorophyll is needed for photosynthesis
Place a destarched variegated plant in sunlight for several hours.
Then test one of its leaves for the presence if starch
What is a variegated leaf
A leaf that only contains chlorophyll in specific areas - causing some parts to appear greener (and others appear white)
Photosynthesis experiments - proving light is needed for photosynthesis
Take a destarched plant and cover part of one of its leaves with black card or tinfoil so light cannot reach that part.
Place the leaf in sunlight for several hours then test the leaf for the presence of starch ( the area covered by the card should show no starch is present)
Photosynthesis experiments - prove carbon dioxide is needed
Take a destarched plant and place it inside a polythene bag
Before sealing the bag add a pot of soda lime (a chemical which will absorb all co2 and water vapour)
Leave the plant in sunlight for several hours then test for startch
Photosynthesis experiments - prove oxygen is given off
Place an upturned test tube above an aquatic plant like pondered
Leave it in sunlight for several hours
When this is done take the tube and place a glowing splint inside it.
The splint will relight showing oxygen is present
Photosynthesis Limiting factors - light intensity
The higher the light intensity, the faster the rate of photosynthesis
This continues until photosynthesis reaches its maximum rate
If light intensity is too low photosynthesis will not occur
What is the effect of Limiting factor (photosynthesis) - carbon dioxide
The greater the carbon dioxide concentration the greater the rate of photosynthesis
As the atmosphere only contains 0.04% carbon dioxide it is often the limiting factor
Farmers artificially change the levels of co2 in greenhouses to increase the rate
It works as a substrate, binding to an enzyme in the light independent stage.
Effect of photosynthesis Limiting factors - temperature
Photosynthesis is an enzyme controlled reaction so if the temperature is too high the enzyme will denature
What is a limiting factor
Factors which can prevent the increase in the rate of a process (e.g photosynthesis)
How do you calculate the rate of photosynthesis
Rate = 1/t
T is time
The unit of rate depends on the time (e.g, s, min, h) and is written as s^-1 (or min^-1 etc…)
How do you calculate light intensity
Light intensity = 1/ (distance from light source)^2
How can you investigate the rate of photosynthesis (pondweed)
At different light intensities:
You measure the volume of oxygen given off by the pondweed in a certain time (using a gas syringe)
Or just count the bubbles given off
How can we study the effect of limiting factors on the rate of photosynthesis
By changing the limiting factors:
Light intensity - place a light source at different distances
Co2 concentration - add different masses of sodium hydrogen carbonate to the water (this will release co2)
Temperature - place the apparatus (used to study rate e.g pondweed experiment) in different temperature water baths
How is DNA stored in the nucleus
All dna has 46 chromosomes (23 pairs)
There are x and y chromosomes, each containing a different number of genes
(X is much larger)
What is one organelle that cant be seen with a light microscope
Ribosomes (too small)
What does the nucleus do
It contains DNA which controls the cells activities / function
What is the purpose of the light / lamp in light microscopes
To make the image easier to see
What is a somatic cell
A body cell (excluding gametes)
What is a germ cell
Cells that create gametes
The cells are diploid, but produce haploid gametes
How can pH of a solution can be controlled
By using a buffer
(pH buffer maintains pH in a narrow range)
Why do both prokaryotes and eukaryotes have ribosomes
As they are not membrane bound organelles, and are needed for protein synthesis
