Topic 1 - Key Concepts In Biology Flashcards
What does resolution mean?
What does it mean if the resolution of an image is higher?
The ability a microscope has to distinguish two objects (that are close together) as separate objects and see detail.
A higher resolution means that the image can be seen more clearly and in more detail.
What are all living things made out of?
Cells
What groups can cells be classed into?
Prokaryotic cells or Eukaryotic cells
What are eukaryotic cells?
Eukaryotic cells are complex and include all plant and animal cells. Eukaryotic cells have membrane bound organelles e.g. nucleus.
What are prokaryotic cells?
Prokaryotic cells are smaller and simpler than eukaryotic cells (e.g. bacteria). Prokaryotic cells don’t have any membrane bound organelles.
What are eukaryotes?
Eukaryotes are organisms that are made up of eukaryotic cells.
What are prokaryotes?
A prokaryote is a prokaryotic cell (they are single-celled).
What are the different parts of a cell called?
Subcellular structures
What are the subcellular structures in animals cells?
Nucleus, Cytoplasm, Cell membrane, Mitochondria, Ribosomes,
What are the subcellular structures in plant cells?
Nucleus, Cytoplasm, Cell membrane, Mitochondria, Ribosomes, Cell wall, Large vacuole, Chloroplasts,
What does a nucleus contain?
A nucleus contains genetic material arranged into chromosomes. The genetic material controls the activities of the cell.
What is the cytoplasm?
A gel-like substance where most of the chemical reactions happen.
What does the cytoplasm contain?
Enzymes that control the chemical reactions taking place in it.
What is the function of the cell membrane?
To hold the cell together and control what goes in and out.
What happens in mitochondria?
Most of the reactions for respiration take place in the mitochondria. Respiration transfers energy that the cell needs to work.
What is the function of ribosomes?
They are involved in the translation of genetic material in the synthesis of proteins (they are where proteins synthesise)
What is the function of the cell wall?
To support the cell and strengthen it.
What is the cell wall made out of?
Cellulose
What does the large vacuole contain?
Cell sap which is a weak solution of sugar and salts.
What is the function of the vacuole?
To maintain the internal pressure to support the cell.
What are chloroplasts?
Where photosynthesis happens which makes food for the plant.
What do chloroplasts contain?
Chlorophyll
What subcellular structures do bacterial cells contain?
Chromosomal DNA, Ribosomes, Cell membrane, Plasmid DNA, Flagellum (plural flagella)
What is the chromosomal DNA in a bacterial cell?
One long circular chromosome.
What is the function of the chromosomal DNA in a bacterial cell?
It controls the cell’s activities and replication.
Where is the chromosomal DNA in a bacterial cell?
It floats free in the cytoplasm (NOT IN A NUCLEUS).
What is plasmid DNA?
Plasmid DNA is small loops of extra DNA in a bacterial cell that aren’t part of the chromosome.
What do plasmids contain?
Genes for things like drugs resistance. These can be passed between bacteria.
What are flagellum?
Long hair-like structures that rotate to make the bacterium move. Flagellum are plural flagella.
What can flagellum be used for?
To move bacterial cells away from harmful substances like toxins and towards beneficial substances such as nutrients or oxygen.
What do multicellular organisms contain?
Multicellular organisms contain lots of different types of cells - cells with different structures.
What are specialised cells?
Cells that have a structure which makes them adapted to their function.
What specialised cells do you need to know about?
Egg cell,
Sperm cell,
Ciliated epithelial cells
What are the main functions of the egg in reproduction?
To carry the female DNA and to nourish the developing embryo in the early stages.
How is the egg cell adapted to its function?
It contains nutrients in the cytoplasm to provide energy for the egg to grow and divide when it’s fertilised.
It has a haploid nucleus (containing one set of chromosomes - 23 in total).
Straight after fertilisation it’s membrane changes structure to prevent any more sperm getting into the egg. This makes sure the offspring gets the correct amount of DNA.
What is another name for the egg cell?
The ovum
What is the only animal cell that you can see with the naked eye (without a microscope)?
The egg (ovum) cell.
What is most of the egg cell made out of?
Most of the egg cell is padding, these layers protect the information in the cell’s nucleus.
The egg cell contains a cell membrane, nucleus, cytoplasm, and mitochondria.
What is the function of a sperm?
To transport the male’s DNA to the female’s egg.
How is sperm adapted to its function?
A sperm cell has a long tail so it can propel itself forward and swim to the egg cell (for locomotion).
It has lots of mitochondria in the mid-piece to provide energy in the form of ATP from aerobic respiration in order to swim the distance to the egg.
It has an acrosome at the front of the ‘head’ where it stores enzymes needed to digest through and penetrate the membrane of the ovum.
It has a haploid nucleus (containing one set of chromosomes - 23 in total).
What is the structure of the sperm cell?
Tail, Middle section/mid-piece, Head, Nucleus, Acrosome,
What do epithelial cells line the surfaces of?
Epithelial cells line the surfaces of organs.
What is the function of ciliated epithelial cells?
To move substances in the body.
How are ciliated epithelial cells used in the lining of airways?
The cuboidal ciliated epithelial cells line the ends of bronchioles in the lungs. Ciliated epithelial cells line the airways and help to move mucus (and all of the particles from the air that it has trapped) up to the throat so it can be swallowed and doesn’t reach the lungs.
How are ciliated epithelial cells adapted to their function?
The cilia move/waft substances in one direction along the surface of the tissue.
How are ciliated epithelial cells used in the Fallopian tubes (oviducts)?
The ciliated epithelial cells can be tall and narrow, making up columnar ciliated epithelium. The cilia move and waft an egg cell from the ovary towards the uterus.
Where are mitochondria stored in the sperm cell?
In the body / mid-piece of the sperm
Approximately how long is a sperm cell without the tail?
60 micrometers
Approximately how long is a sperm cell with the tail?
120 micrometers
What are cilia?
Cilia are hair-like structures that move substances in the body. Cilia are covered in cell membrane and contain strands of a substance that can contract and cause waves of movement.
What are sperm cells and egg cells called as a pair?
Sex cells / gametes.
Whet do fertilised egg and sperm cells fuse to make?
A zygote which then develops into an embryo
How do microscopes effect images?
Microscopes use lenses to magnify images and microscopes also increase the resolution of images.
When were light microscopes invented?
In the 1590s
How do light microscopes work?
By passing light through the specimen and using two types of magnification lenses - a concave lens and a convex lens.
What do light microscopes allow us to do?
View subcellular structures such as nuclei and chloroplasts. Light microscopes also allow us to study living cells.
When were electron microscopes invented?
In the 1930s
What do electron microscopes use to work?
Electrons rather than light
How are electron microscopes different to light microscopes?
Electron microscopes have a higher magnification and resolution than light microscopes so they allow us to see much smaller structures in greater detail. For example the internal structure of mitochondria and chloroplasts.
What have electron microscopes allowed us to do?
To have a greater understanding of how cells work and the role of subcellular structures.
What can electron microscopes not be used to view?
Living cells (unlike light microscopes)
What is the method of viewing a specimen using a light microscope?
1) Take thin slice of the specimen (to let light through it).
2) Take a clean slide and use a pipette to place one drop of water onto the middle of the slide (this will secure the specimen in place). Then use tweezers to place the slice of specimen of the slide.
3) Add one drop of stain if the slice of specimen is transparent or colourless as this makes the specimen easier to see. Different stains must be used to highlight different subcellular structures within cells.
4) Place a cover slip at one end of the specimen, using a mounted needle to hold it at an angle then carefully lower the cover slip onto the slide. Press the cover slip down gently to remove any air bubbles then clip the slide onto the stage.
5) Choose the lowest-powered objective lens - this will be the smallest lens.
6) Using the course adjustment knob, move the stage up so that the slide is just underneath the objective lens. Next look down the eyepiece and move the stage downwards until the specimen is nearly in focus - DO NOT MOVE THE STAGE TOO CLOSE TO THE LENS OR IT WILL SMASH THE SLIDE.
7) Adjust the focus with the fine adjustment knob until the image is focused. Use a clear ruler to measure the diameter of the circular area visible (the field of view - FOV)
8) To view the specimen in a greater magnification, swap to a higher-powered objective lens, refocus and recalculate the field of view.
What does measuring your field of view allow you to do?
Estimate the size of the specimen.
If your field of view was originally 5 mm, then you swap to a lens which is 10x more powerful than the lens you started with, what will your field of view be now?
5 mm / 10 = 0.5 mm
What is the method of drawing a scientific drawing of a specimen which has been viewed using a microscope?
1) Use a sharp pencil and draw outlines of the main features of the specimen using clear, unbroken lines. Do not include any colouring or shading.
2) Make sure that your drawing takes up at least half of the space available and remember to keep all of the parts in proportion.
3) Label the important features of the diagram with straight lines (no arrowheads) which don’t cross over each other. Include a magnification and a scale.
4) Add a title, date and a scale to show magnification
5) The drawing must take up more than 50% of the paper and high power diagrams must include a few adjacent cells
What are the features on a light microscope?
- Eye piece lens (ocular lens)
- Objective lenses (low, medium and high power)
- Stage with stage clips.
- Lamp
- Mirror
- Base
- Fine adjustment knob
- Spine
- Coarse adjustment knob
What is the function of the coarse focus on the microscope?
Moves the stage or to aid focussing.
What is the function of the fine focus on the microscope?
Moves the stage (a small amount) to aid focussing.
What is the function of the mirror on the microscope?
Reflects light from the light source up through the stage.
What is the function of the objective lens on the microscope?
Magnifies the specimen, makes the specimen appear larger.
What is the function of the stage on the microscope?
Supports and positions the slide for focussing.
How do you find out the total magnification when using microscopes?
- Read the magnification on the eye piece.
- Read the magnification on the objective lens.
- Multiply the magnification from the eye piece with the magnification from the objective lens to get the total magnification.
How do you prepare a slice for an onion cell microscope slide?
1) Take a piece of onion and peel away the skin in the inside surface using your fingernails or forceps.
2) From the skin you have removed cut a small piece (no more than about 5 mm square).
3) Place a drop or two of water in the centre of a microscope slide, then place the onion skin on the water drop(s).
4) Using a mounting needle, carefully lower a coverslip onto the onion skin. Take care to avoid air bubbles.
5) At one end of the coverslip Place a drop of iodine solution and at the other, a paper towel. The iodine should be drawn under the coverslip, staining the onion skin. Take care not to get iodine in your hands. Wear eye protection.
6) View the onion skin using a microscope, and draw your observations.
What does “mm” stand for?
Millimetre
What does “μm” stand for?
Micrometre
What does “nm” stand for?
Nanometre
What does “pm” stand for?
Picometre
What is 1 mm in m?
0.001 m or 1 x 10^-3 m
What is 1 μm in m?
0.000001 m or 1 x 10^-6 m
What is 1 nm in m?
0.000000001 m or 1 x 10^-9 m
What is 1 pm in m?
0.000000000001 or 1 x 10^-12
How do you convert millimetres to micrometres?
Multiply by 1000
How do you convert micrometres to nanometres?
Multiply by 1000
How do you convert nanometres to picometres?
Multiply by 1000
How do you convert picometres to nanometres?
Divide by 1000
How do you convert nanometres to micrometers?
Divide by 1000
How do you convert micrometres to millimetres?
Divide by 1000
How do you convert metres to millimetres?
Multiply by 1000
How do you convert millimetres to metres?
Divide by 1000
What is a millimetre as a fraction of a metre?
1000th if a metre
What is a micrometre as a fraction of a metre?
1000, 000th of a metre
One millionth
What is a nanometre as a fraction of a metre?
1000,000,000th of a metre
One billionth
What is a picometre as a fraction of a metre?
1000,000,000,000th of a metre
One trillionth
What is magnification?
The degree to which the size of an image is larger than the object itself, expressed as x100 etc.
What is the maximum magnification for a light microscope?
X 1500
What is the maximum magnification for an electron microscope?
X 500,000
What is the maximum resolution for a light microscope?
200 nm
What is the maximum resolution for an electron microscope?
0.20 nm
In electron microscopy what are used as stains?
Metal particles or metal salts. The images produced afterwards are always black, white and grey. Colour is added afterwards and these images are called “false-colour” electron micrographs.
What is the magnification equation using image size and actual size?
I
——-
A M
Magnification = image size / actual size
What is the magnification equation using the scale bar?
Magnification = length of scale bar / length the bar represents
How big are the red blood cells of humans?
About 8 micrometres
It would take 1250 of them placed in a row as a flat line to make 1cm
What are some key points about enzymes?
- They are specific
- They are biological catalysts
- They are affected by high temperatures
- They are made of protein which is made from many amino acid molecules joined together.
- There are three main types of enzyme: carbohydrases, proteases and lipases.
- enzymes only speed up the useful chemical reactions in the body whereas high temperatures also speed up the unwanted reactions
What are enzymes made of?
Protein which is made from many amino acid molecules joined together.
What are the three main types of enzymes?
- Carbohydrates
- Proteases
- Lipases
What is diffusion?
Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration.
What states of matter does diffusion take place in? Why?
Liquids and gases, this is because particles in these substances are free to move about randomly.
What is osmosis?
Osmosis is the net movement of water molecules across a partially permeable membrane from a region of higher water potential to region of lower water potential.
OR
Osmosis is the net movement of water molecules across a partially permeable membrane from a region of lower solute concentration to region of higher solute concentration.
Osmosis is a type of diffusion.
What will happen to an animal cell in a hypotonic solution?
It will lyse (burst) due to too much water entering the cell. The concentration of water outside of the cell is greater than the concentration of water inside the cell so due to osmosis the cell will gain more water. As animal cells don’t have cell walls the water cannot be contained and the cell membrane bursts.
What will happen to an animal cell in a isotonic solution?
The animal cell will be normal as the concentration of water inside the cell is equal to the concentration of water outside of the cell.
What will happen to an animal cell in a hypertonic solution?
It will shrivel as the concentration of water inside the cell is greater than the concentration outside the cell (in the hypertonic solution) so due to osmosis the animal cell will lose water and shrivel.
What is a hypotonic solution?
Pure water
What is an isotonic solution?
When two solutions are at the same concentration it is an isotonic solution (a weak solution).
What is a hypertonic solution?
A concentrated solution.
What will happen to a plant cell in a hypotonic solution?
It will be turgid (normal) as water diffuses from the hypotonic solution into the cell by osmosis due to the concentration of water outside of the cell being greater than the concentration inside the cell. The plant cell starts to swell, but the cell wall prevents it from bursting. It becomes turgid and the pressure inside the cell rises until this internal pressure is equal to the pressure outside.
What will happen to a plant cell in a isotonic solution?
It becomes flaccid. The concentration inside and outside of the cell is equal so the plant has less water than normal (when it is turgid). The loss of water makes the cell limp and the cell membrane begins to shrink away from the cell wall due to less pressure in the cell.
What will happen to a plant cell in a hypertonic solution?
It will be plasmolyzed as the concentration of water inside the cell is greater than the concentration of water outside of the cell so due to osmosis the plant cell will lose water. This leads to the plant cell becoming limp and the cell membrane shrinking away from the cell wall.
What is active transport?
the movement of particles across a membrane against a concentration gradient (from an area of lower concentration to an area of higher concentration) using energy transferred during respiration.
What does active transport require?
Energy in the form of ATP made from respiration (in mitochondria).
How does active transport work?
Transporter proteins transport molecules outside the cell (where the concentration is lower) to the inside of the cell (where the concentration is higher).
What is an example of when active transport is used?
When minerals are taken into root hair cells.
What is an important point to remember when using magnification equations?
Both measurements of real size and image size should be in the same units. They will need to be converted to the same.
What is a catalyst?
A substance which increases the speed of a reaction without being changed or used up in the reaction.
How can you usually increase the speed of a reaction (without enzymes)?
What is a disadvantage of this?
By raising the temperature
A disadvantage is that this would speed up the unwanted reactions as well as the useful reactions.
What do chemical reactions usually involve?
Substances being split apart or joined together.
What is the substrate?
The molecule changed in the reaction.
What is the active site on enzymes?
The part where the enzyme joins on to its substrate to catalyse the reaction.
How many substrates do enzymes usually work with?
Only one - enzymes are said to have a high specificity for their substrate.
Why do enzymes have a high specificity for their substrate?
For the enzyme to work the substrate had to fit into the active site. If the substrate’s shape doesn’t match the active site’s shape then the reaction won’t be catalysed. This is called the “lock and key” mechanism or the enzyme substrate complex.
What is the “lock and key” mechanism/ the enzyme substrate complex?
That the substrate has to fit into the enzyme’s active site for the reaction to be catalysed because the substrate fits into the enzyme just like a key fits into a lock.
How do higher temperatures affect the rate of reaction when enzymes are involved?
A higher temperature increases the rate of reaction at first however if the temperature gets too hot then some of the bonds holding the enzyme together break. This changes the shape of the enzyme’s active site so the substrate no longer fits. The enzyme is denatured.
What happens when an enzyme is denatured?
A factor (temperature or pH) changes the shape of / interferes with the bonds holding an enzyme together. This changes the shape of the active site so the substrate won’t fit the active site anymore. The enzyme is denatured.
How does pH affect the rate of reaction when enzymes are involved?
If the pH is too high or too low the pH interferes with the bonds holding the enzyme together. This changes the shape of the active site and denatures the enzyme.
What is often the optimum pH for enzymes?
7 (neutral)
What is pepsin?
An enzyme used to break down proteins in the stomach.
What pH does pepsin work best at?
Why?
pH 2 because it is well suited to the acidic conditions in the stomach.
How does substrate concentration affect the rate of reaction when enzymes are involved?
- The higher the substrate concentration, the faster the rate of reaction.
- This is because if the substrate concentration is higher then it is more likely that an enzyme will react with a substrate molecule. However, once all of the enzymes’ active sites are full then increasing the concentration of substrate molecules doesn’t change the rate of reaction as there are no more enzymes to catalyse the reaction.
What does the graph look like for how temperature affects the rate of reaction with enzymes?
- Initially the graph has a curve with a steady increase.
- The curve begins to decrease when the enzyme’s optimum temperature is reached (around 40°C).
- Finally the rate of reaction suddenly decreases (the line becomes vertical.)
- the peak of the curve is the optimum temperature, where the enzyme is most active
What does the graph look like for how pH affects the rate of reaction with enzymes?
- The graph is a parabola.
- Initially the graph has a curve with a steady increase.
- Once the optimum pH is reached the curve steadily decreases.
What does the graph look like for how substrate concentration affects the rate of reaction with enzymes?
- The rate of reaction steadily increases (with a straight line) until it reaches the point when all of the enzyme’s active sites are full.
- The rate of reaction then stays the same (as a straight horizontal line).
Which enzyme catalyses the break down of starch to maltose?
Amylase
Which chemical solution is used to detect starch?
Iodine
What colour will iodine change to if starch is present?
From browny-orange (the colour of iodine) to blue-black.
What is the method for investigating how pH affects enzyme activity?
1) Put one drop of iodine solution into every well of a spotting tile.
2) Place a Bunsen burner on a heat-resistant mat and a tripod and gauze over the Bunsen burner. Put a beaker of water on top of the tripod and heat the water until it is 40°C by using a thermometer. Keep the temperature of the water constant throughout the experiment. An electric water bath could be used instead of the Bunsen burner and beaker of water.
3) Using a syringe, add 3cm^3 of amylase solution and 1cm^3 of a solution with particular pH to a boiling tube. Put the boiling tube into the beaker of water and wait for 5 minutes.
4) Use a different syringe to add 3cm^3 of a starch solution to the boiling tube.
5) Immediately mix the contents of the boiling tube together and start a stopwatch.
6) Every 10 seconds sample the solution to record how long it takes for the amylase to break down the starch - use a pipette to add fresh samples of solution every 10 seconds to the iodine in the spotting tile. Once the iodine remains orange-brown starch is no longer present and the amylase has broken down all the starch.
7) Repeat the experiment with solutions of different pHs to see how pH affects the time taken for the starch to be broken down.
8) To keep the experiment a fair test variables should be controlled e.g. the volume and concentration of amylase each time the experiment is repeated.
a pH meter could be used to accurately measure the pH of the solutions
How can you calculate the rate of reaction in experiments which measure how much something changes over time?
By dividing the amount that it has changed by the time taken.
What is the formula for calculating the rate of reaction for the experiment investigating the effect of pH on enzyme activity?
Rate = 1000 / time
Units = s ^-1 (meaning per second)
What are lipids?
Fats and oils
What do plants store energy in the form of?
Starch
What happens to starch in plants when plants need energy?
The enzymes break down the starch into smaller molecules (sugars) which can then be respired to transfer energy to be used by the cells.
Which enzymes convert carbohydrates into simple sugars?
Carbohydrases
What is an example of a carbohydrase?
Amylase
Which enzymes break down proteins into amino acids?
Proteases
Which enzymes break down lipids into glycerol and fatty acids?
Lipases
How can carbohydrates be synthesised?
By joining together simple sugars.
Which enzyme joins together chains of glucose molecules to make glycogen?
Glycogen synthase
What is glycogen?
A molecule used to store energy in animals
How are proteins made?
By joining amino acids together, enzymes catalyse the reaction needed to do this
How do you test for reducing sugars?
By adding Benedict’s reagent (which is blue) to a sample and heating it in a water bath at 75°C. If the test is positive a coloured precipitate will be formed.
What will be formed if the test for reducing sugars using Benedict’s reagent is positive?
A coloured precipitate
What is a precipitate?
Solid particles suspended in solution
What is the initial colour of the precipitate when testing for reducing sugars using Benedict’s reagent (for no sugar)?
Blue
What is the second colour of the precipitate when testing for reducing sugars using Benedict’s reagent (for the lowest amount of sugar with some still present)?
Green
What is the third /middle colour of the precipitate when testing for reducing sugars using Benedict’s reagent (for the intermediate amount of sugar)?
Yellow
What is the fourth / penultimate colour of the precipitate when testing for reducing sugars using Benedict’s reagent (for the second highest amount of sugar)?
Orange
What is the final colour of the precipitate when testing for reducing sugars using Benedict’s reagent (for the highest amount of sugar)?
Brick red
What is the colour changing sequence for how the colour of the precipitate changes depending on the amount of sugar present in the test for reducing sugars?
Blue, green, yellow, orange, brick red
What is iodine solution made of?
Iodine dissolved in potassium iodide solution
How do you test for lipids?
State and describe how.
Using the emulsion test
1) Shake the test substance with ethanol for about 1 minute until it dissolves, then pour the solution into water.
2) If there are any lipids present they will precipitate out of the liquid and show up as a milky emulsion.
3) The more lipid there is, the more noticeable the precipitate will be.
How do you test for proteins?
State and describe how.
By using the biuret test
1) First, add a few drops of potassium hydroxide solution to make the solution alkaline.
2) Then add some copper (II) sulfate solution (which is bright blue) - if there is no protein then the solution will remain blue, if protein is present then the solution will change to purple.
Or you can use biuret solution which is a mixture of sodium/potassium hydroxide and copper sulfate.
What is calorimetry?
When food is burnt to see how much energy it contains
What is the active site?
Where the substrate molecule fits during the reaction
What is the optimum pH?
Where the rate of reaction is fastest.
what stain can be used to stain DNA to view using a light microscope?
Methylene blue
what units are used for rate of reaction?
s^-1
what happens to the pH of the solution fatty acids are in when lipids are broken down into fatty acids and glycerol?
the fatty acids lower the pH of the solution they are in
what is the synthesis of molecules?
joining smaller components together to make larger molecules, e.g. joining together amino acids to make protein
how can molecules be synthesised?
by using enzymes to catalyse the reactions needed for synthesis
what is an example of a reducing sugar?
glucose
what is an emulsion?
when one liquid doesn’t dissolve in another - it just forms little droplets
how do you carry out a calorimetry experiment?
1) You need a dry food because it will burn more easily, for example dried beans or pasta will work best
2) weigh a small amount of the food and then skewer it on a mounted needle
3) next, add a set volume of water to a boiling tube (held with a clamp) - this will be used to measure the amount of energy that’s transferred when the food is burnt
4) measure the temperature of the water, then set fire to the food using a Bunsen burner flame, making sure that the Bunsen burner isn’t too near to the water because it may interfere with the results
5) immediately hold the burning food under the boiling tube until it goes out. then relight the food and hold it under the tube again - repeat this until the food won’t catch fire again
6) finally, measure the temperature of the water again and use the result to calculate the joules of energy the food contains using the formula
7) you can minimise the energy in the food being transferred to the environment by insulating the boiling tube e.g. with foil
how do you work out the joules of energy in the food in calorimetry?
energy in food (in j) = mass of the water (in g (same as 1cm^3)) x temperature change of water (in °C) x 4.2
how doh you work out how many joules are in each gram of food in calorimetry?
energy per gram of food (in J/g) = energy in food (in J) / mass of food (in g)
what types of molecules can diffuse through cell membranes? what types of molecules cannot?
only very small molecules can diffuse through cell membranes e.g. glucose, amino acids, water and oxygen
larger molecules such as starch and proteins cannot fit through the membrane
what is a partially permeable membrane?
a membrane with very small holes in it so only small molecules can pass through and not larger molecules
in which direction do water molecules pass through the partially permeable membrane during osmosis?
the water molecules pass both ways through the membrane because the water molecules move about randomly all the time, however, because there are more water molecules on one side than the other there’s a steady net flow of water molecules from one region to the other
how do you carry out an experiment to investigate osmosis?
1) prepare sucrose solutions of different concentrations ranging from pure water to a very concentrated sucrose solution.
2) use a cork borer to cut a potato into the same sized pieces (the pieces need to be about 1cm in diameter and from the same potato.)
3) divide the potato cylinders into groups of three and use a mass balance to measure the mass of each group.
4) place one group in each solution
5) leave the cylinders in the solution for at least 40 minutes making sure that all of the cylinders get the same amount of time in the solution
6) remove the cylinders and pat them dry gently with a paper towel. this removes excess water from the surface of the cylinders so you get a more accurate measurement of their final masses.
7) weigh each group again and record your results
8) use your results to calculate the percentage change in mass for each group of cylinders before and after the time in the sucrose solution.
how do you calculate the percentage change in mass in an experiment?
percentage change in mass = (final mass - initial mass) / initial mass x 100
a positive result shows a gain in mass and a negative result shows a loss of mass
What is an example of a prokaryotic cell?
Bacteria
What is the formula for total magnification?
Total magnification = eyepiece lens magnification x objective lens magnification
how do you work out total magnification using the magnification of the eyepiece lens and the objective lens?
total magnification = eyepiece lens magnification x objective lens magnification
What are three examples of big molecules?
Why would these molecules need to be broken down into their smaller components?
Proteins, lipids and carbohydrates, these molecules need to be broken down so they can be used for growth and other life processes
Why do digestive enzymes need to break down the molecules in food?
- Many of the molecules in the food we eat are too big to pass through the walls of our digestive system so digestive enzymes break them down into smaller, soluble molecules to allow the molecules to pass easily through the walls of the digestive system, allowing them to be absorbed into the bloodstream.
- The molecules can then pass into cells to be used in the body.
If something moves from an area if higher concentration to an area of lower concentration has it moved up or down the concentration gradient?
Down (along) the concentration gradient
What is an example of when active transport is used in the digestive system?
- when there is a higher concentration of nutrients in the gut than in the blood, the nutrients diffuse naturally into the blood
- however if there is a lower concentration of nutrients in the gut than in the blood active transport allows nutrients to be taken into the blood despite going against the concentration gradient.
- this is essential to prevent starvation
What is M?
A unit of concentration (mol dm^-3). You will see this unit in the core practical to investigate osmosis. A solution with a concentration of 0.0M of sucrose solution is pure water.
What are some control variables for the core practical investigating osmosis?
The volume of solution in each group, the size of the potato cylinders, the type of potatoes used, the amount of drying
What is the independent variable in the core practical investigating osmosis?
The sucrose solution concentration
What does calculating the percentage change in mass allow you to do in the core practical investigating osmosis?
To compare the effect of the sucrose concentration on cylinders that didn’t have the same initial mass
In the core practical investigating osmosis, what does it mean if the points plotted on the graph are above the x-axis?
The water concentration of the sucrose solutions is higher than in the cylinders. The cylinders gain mass as water is drawn in by osmosis
In the core practical investigating osmosis, what does it mean if the points plotted on the graph are below the x-axis?
The water concentration of the sucrose solutions is lower than in the cylinders. This causes the cylinders to lose water so their mass decreases.
In the core practical investigating osmosis, what does it mean where the curve crosses the x-axis?
The fluid inside the cylinders and the sucrose solution are isotonic - they have the same water concentration
What is the average size of a unicellular organism?
200μm
What is the average diameter of a plant cell?
40μm
What is the width of a very fine human hair?
30μm
What is the average diameter of an animal cell?
20μm
What is the average diameter of a mitochondrion?
1μm
What is the average diameter of a bacterium?
0.5 -1μm (500-1000nm)
What is the size of the smallest object visible with a light microscope?
0.2μm (200nm)
What is the average diameter of a ribosome?
20nm
What is the average thickness of a membrane?
7nm
What is the diameter of a DNA molecule?
2nm
What is the size of the smallest object visible with an electron microscope?
0.5nm
What is the diameter of a hydrogen atom (the smallest atom)?
0.04nm
Who was one of the first people to examine cells using a microscope?
Robert Hooke
What is an example of a non-reducing sugar so therefore you couldn’t test for using the Benedict’s test?
Sucrose
What does “c.” mean?
“Approximately”, this symbol stands for “circa” is put before a number to indicate that it is only approximate
If a food test is qualitative what does this mean?
The test only shows whether the substance is present or not.
If information is quantitative what does this mean?
The mass or volume of the substance is given
What is an example of a semi-quantitative food test?
The Benedict’s test, it gives information about value, often in terms of ‘little’, ‘some’ or ‘lots’, or approximate values
What are halophytes?
Plants that are adapted to live in salty areas, their roots take in large amounts of salts from the soil which helps osmosis to continue from the soil into the plant. Halophytes get rid of the extra salt they absorb in various ways
Why is sucrose used in the solutions in the core practical test for osmosis?
The sucrose molecules are too large to diffuse through cell membranes so only the movement of water is being tested
