biology a level 2022 paper 1 2023 with verified questions and answers

what is simple diffusion molecules pass directly through the plasma membrane without the assistance of another molecule, from a higher concentration to a lower concentration. when is simple diffusion used to allow molecules to travel in and out of the cell membrane: examples water, o2, co2 and ethanol. What is a phospholipid? It is a lipid that has a phosphate group attached to the glycerol and only two fatty acid chains. What is a protein? chain of amino acids What is a glycoprotein? protein with carbohydrate attached What is a glycolipid? lipid with carbohydrate attached Function of glycoproteins cell-cell recognition glycolipid function cell recognition protein functions structural support, storage, transport, cellular communications, movement, and defense against foreign substances What is the fluid mosaic model? states that a membrane is a fluid structure with a "mosaic" of various proteins embedded in it What is cholesterol? A waxy, fat like substance what is the function of cholesterol it regulates the fluidity of the membrane, preventing it from becoming too fluid or too stiff used to make the hormones oestrogen, testosterone and vitamin D What is facilitated diffusion? Movement of specific molecules across cell membranes through protein channels When is facilitated diffusion used? when molecules are too large to fit between phospholipids What is osmosis? diffusion of water across a selectively permeable membrane from higher concentrations to lower concentrations. When is osmosis used? when water diffuses into a plant cell. When is active transport used? When substances need to be moved against the concentration gradient What is active transport? the movement of ions or molecules across a cell membrane into a region of higher concentration, assisted by enzymes and requiring energy. What is used in active transport for energy? ATP When are carrier proteins used? active transport What is a carrier protein? a transport molecule, change shape to allow the molecule to pass across the membrane What is a channel protein? An intrinsic protein that forms a water-filled pore in the membrane, allowing specific polar molecules to diffuse through - when certain ions bind to the protein it will open What is co-transport? The transport of one substance coupled with the transport of another substance across a plasma membrane in the same direction though the same protein carrier How does co-transport work? - Na ions are actively transported out of the epithelial cells by the sodium-potassium pump, into the blood - there is a higher concentration of Na ions in the lumen of the intestine than in the epithelial cells - Na ions move down their concentration gradient into the epithelial cells through a co-transport protein - as they diffuse through this protein, they carry either amino acid or glucose molecule into the cell with them - the glucose/amino acids pass into the blood plasma by facilitated diffusion (against their concentration gradient) How are cells adapted to maximise the rate of transport across their membranes? there can be an increase in the amount of protein channels and protein carriers, and also an increase in the surface area. How does surface area affect the rate of transport? the larger the system, the more places that allow transport, therefore it will happen more. What is a calibration curve? A graph constructed from the data collected on solutions of known concentrations. what is required practical 3? 1. make a serier of dilutions of 1m of sucrose solution. These should be at 0.0,0.2,0.4,0.6,0.8,1.0 and diluted using distilled water. 2. measure 5cm3 of each dilution into separate tubes 3. use a cork borer to cut out six potato chips, dry each chip using a paper towel but do not squeeze. 4. weigh each chip to make sure they are the same and to record their starting weight before the experiment. 5. place a potato chip in each test tube and leave for 20 mins. 6. remove each potato chip and dry them again, and then weigh them again. 7. calculate the percentage change in mass for each dilution of the solutions. conclusion of required practical 3 potato chips in lower concentrations of glucose will increase in mass, in higher concentrations of glucose they will decrease in mass. This is because the dilute (less glucose to water) glucose solutions have a higher WP than the potato, so the water will passively move via osmosis to the potato. In the highly concentrated solutions, the water will move out of the potato, so it will decrease in mass. what are the components of a eukaryotic cell? rough endoplasmic reticulum; smooth endoplasmic reticulum; ribosomes; mitochondria; chloroplasts; lysosomes; centrioles; golgi apparatus; what are the components of a prokaryotic cell? Flagellum, single circular chromosome, ribosomes, cytoplasm, plasmids, cell membrane, cell wall What is the cell surface membrane? The plasma membrane that surrounds cells and forms the boundary between the cell cytoplasm and the environment. What is the function of the nucleus? Contains the cell's genetic material and controls the cell function of mitochondria? generate most of the chemical energy needed to power the cell's biochemical reactions. Chemical energy produced by the mitochondria is stored in a small molecule called adenosine triphosphate (ATP). components of mitochondria their own circular DNA and ribosomes, double layered membrane What are chloroplasts? Membrane-bound organelles where photosynthesis takes place in plants What is the golgi apparatus? flattened stacks that process, package, and deliver proteins and lipids from the ER What is a Golgi vesicle? A small fluid-filled sac in the cytoplasm, surrounded by a membrane and produced by the golgi apparatus What are lysosomes? Small organelles filled with (digestive) enzymes. Breaks down lipids, carbohydrates, and proteins into small molecules that can be used by the rest of the cell. What are ribosomes? site of protein synthesis (where proteins are made) What is the endoplasmic reticulum? Rough- holds ribosomes, smooth, does not have ribosomes. This is the internal delivery system of the cell Function of cell wall Strengthens and protects the cell function of vacuole Stores materials such as water, salts, proteins and carbs; helps plants support heavy structures like leaves function of cytoplasm in a prokaryotic cell? medium for chemical reactions, lacks membrane bound organelles what type of ribosomes do prokaryotic cells contain? smaller Does a prokaryotic cell have a nucleus? No nuclear membrane or nucleoli, they have a single circular dna molecule that floats in the cytoplasm, and is not associated with proteins. what is the cell wall for in prokaryotic cells? made of murein, a glycoprotein what may a prokaryotic cell also contain? one or more plasmids, a capsule surrounding the cell, one or more flagella. What is plasmid DNA? a small section of DNA that can replicate independently of chromosomal DNA What is a capsule? material surrounding the cell outside the cell wall consisting of polysaccharidesor protein. It serves to protect the cell. What is flagella? Long, thin whip-like structure that helps organisms move through moist or wet surroundings What is a virus? a tiny, nonliving, particle that enters and reproduces inside a living cell (host cell) what is an optical microscope? light microscope What is cell fractionation? The process where cells are broken up and the different organelles they contain are separated out. how would you carry out cell fractionation? the tissue must be first placed in a cold, isotonic buffer solution. then there are two stages to cell fractionation: homogenation and ultracentrifugation. Why should the solution be isotonic? To prevent damage to the organelles through osmosis so that it is of the same water potential as the tissue why should the solution be cold? to reduce enzyme activity, that might break down the organelles Why should the solution be buffered? so that there are no changes in the pH, which could alter the structure of the organelles and affect the functioning enzymes. what is homogenisation? cells are broken up by a homogeniser, which releases the organelles from the cell. There will be a resultant fluid, called a homogenate, which will then be filtered to remove any complete cells and cell debris. What is ultracentrifugation? The process by which the fragments in the filtered homogenate are separated in a machine called a centrifuge. This spins the tubes of homogenate at a very high speed. order of centrifugation? the tube is placed in the centrifuge and spun at a slow speed, the heaviest organelles (nuclei) are forced to the bottom of the tube where they will form a pellet. The fluid that is left at the top of the tube (supernatent) is removed, so just the pellet is left. The supernatent is then placed in another tube and spun in the centrifuge at a faster speed than before, to remove the smaller organelles. The next heavier cells, which would be the mitochondria will be forced to the bottom of the cell. The process is continued, so that with the next increase in speed, the next heaviest organelle is forced into a pellet at the bottom. What is magnification? How much bigger the image is that the specimen what is image size? physical dimensions of an image How do you work out magnification? size of image/size of real object What is resolution? The ability to clearly distinguish the individual parts of an object what happens to resolution as magnification increases The resolution can sometimes suffer, as the image is getting bigger but the quality remains the same. what is the electron microscope? a microscope with high magnification and resolution, employing electron beams in place of light and using electron lenses. How does an electron microscope work? It passes electrons at a shorter wavelength, rather than light through the specimen and can give much better resolution. the electrons are negatively charged, so the electrons can be focused using an electromagnet. what are the two types of electron microscope transmission electron microscope and scanning electron microscope How does a transmission electron microscope work? it works by aiming an electron beam at a thin section and transmitting the beam through it what type of image do you get from a TEM? a photomicrograph, on the screen what is the revolving power of a tem? 0.1nm Limitations of TEM - living specimens cannot be analysed as the whole system must be in a vacuum - image is B&W (and a complex staining process is required) - specimen must be extremely thin - image may contain artefacts - image is 2D What is an SEM microscope? a microscope that scans the SURFACE of an object with a beam of electrons. The electrons bounce off the object. It magnifies up to approximately 100,000x Limitations of SEM -lower resolution than TEM -only the surface of an object can be viewed resolving power of SEM 20nm What is a light microscope? A microscope that uses a series of glass lenses and visible light to magnify an image. This microscope magnifies images up to 1,000 times the actual size. Limitations of light microscope Cannot resolve much of the organelles or internal anatomy, because of poor resolution and lower magnification. how do you measure the size of objects using a light microscope? using an eyepiece graticule, What is an eyepiece graticule? a glass disc that fits on top of the eyepiece lens that is marked with a fine scale from 1 to 100 How do you calibrate an eyepiece graticule? calibration -place stage micrometer on the stage of a microscope -focus on the scale on the stage micrometer using the low power objective lens -align the scales of the eyepiece graticule and stage micrometer -count the number of divisions on the eyepiece graticule that are equivalent to 100 micrometers on the stage micrometer -calculate the length of one eyepiece division -repeat for the medium and high power objective lens What is the nuclear envelope? double membrane that surrounds the nucleus What are nuclear pores? Many opening called nuclear pores extend through the nuclear envelope. Nuclear pores control the movement of substances between the nucleus and the cytoplasm. What is nuceloplasm? cytoplasm and nucleus What is the cristae of the mitochondria? The layers of the folded inner membrane. what is the matrix of the mitochondria? fluid inside cristae What does the matrix contain? protein fibers, water, minerals, nutrients, waste products What does the cristae contain? Enzymes that function in oxidative phosphorylation (energy transformation sites) what is the chloroplast envelope? - double plasma membrane - highly selective in what enters and leaves What are grana? stacks of thylakoids What are thylakoids? coin-shaped, membrane-enclosed compartments inside the grana What are stroma? fluid that surrounds the grana What is chlorophyll? A green pigment found in the chloroplasts of plants, algae, and some bacteria what is genetic diversity? The number of different alleles of genes in a species or population. what does genetic diversity allow to occur? natural selection what is a random mutation random changes in DNA sequence. Can be due to radiation, chemicals, replication error ...etc. Are mutations always harmful? No, some are helpful and some are neutral. A lot of our traits come from mutations what is an advantageous allele an allele inherited by the next generation, which has advantageous characteristics for survival purposes. how does a new allele increase in frequency over generations? if the advantageous allele is carried on through reproduction, there are more offspring with the allele that will transfer it onto the next generation via reproduction. What is directional selection? selection which occurs when a phenotype at one extreme is at a disadvantage What is antibiotic resistance? when an antibiotic has lost its ability to effectively control or kill bacterial growth what is stabilising selection? when the environment favours those with the most common characteristic - those on the extreme dies out the common characteristic increases in proportion the range (standard deviation) will reduce What does natural selection result in? species that are better adapted to their environment what type of adaptations can natural selection result in? behavioural, physical and anatomical what is required practical 6? the use of aseptic techniques to investigate the affects of antimicrobial surfaces on microbial growth procedure of required practical 6 wipe down the surfaces, use a bunsen burner to draw any of the microbes away from the culture using convection currents. flame the wire hoop before using it to transfer bacteria. flame the neck of any bottles to prevent any bacteria. close all windows. after aseptic techniques, what is next in required practical 6? carry out aseptic techniques, then use a sterile pipette to transfer bacteria from the broth to the agar plate. Spread the bacteria evenly using a sterile plastic spreader. use sterile forceps to place a multi disc antibiotic ring on the plate. the ring should only be moved by the center not the arms. Lightly tape a lid on, invert and incubate 25 degrees for 48 hours. do not tape around the whole dish, this will prevent oxygen entering and promote the growth of more anaerobic bacteria. sterilise equipment and disinfect surfaces. what happens after incubation in required practical 6? measure the diameter of the inhibition zone, do not remove the lid. work out the area of the inhibition zone. conclusion of required practical 6? larger inhibition zone means more bacteria has been killed, which means the antibiotic is more effective. if there is a small inhibition zone, the bacteria may be more resistant. what are the adaptations for gas exchange in humans large surface area of alveoli, good blood supply, short diffusion distance, moist surfaces. how does a large surface area of the alveoli increase gas exchange there are many alveoli, which means diffusion can happen more often, therefore increasing gas exchange. How does a good blood supply improve the efficiency of gaseous exchange? many capillaries surround the alveolus, so there can be a constant supply of blood. how does a short diffusion distance in humans make gas exchange more efficient? walls of the alveoli and capilaries are both one cell thick. This means that oxygen can diffuse in a high speeds because it has less distance to travel, and carbon dioxide can diffuse out. how do moist surfaces aid in gaseous exchange the liquid on the surface of the alveoli dissolves gases and facilitates diffusion. How are insects adapted for gas exchange? - Trachae - Spiracles - tracheoles - Short diffusion pathway - Diffusion is in gas phase which is faster how is the trachae adapted for efficient gas exchange the trachae is an evolved network of tubes, which is strengthened by rings to prevent them from collasping. these trachae divide into smaller dead end tubes called tracheoles. What are tracheoles? The very small ends of the trachea where oxygen enters the cells. how does a diffusion gradient aid efficient gas exchange in insects when the cells respire, oxygen will be used up, so the concentration falls. This creates a diffusion gradient, which causes oxygen from the atmosphere to diffuse along the trachae and tracheoles and into the cells. Co2 being produced will create a diffusion gradient in the other direction. This causes co2 to diffuse along the tracheoles and trachae from the cells and to the atmosphere. Respiratory gases are exchanged the quickest in the air, so it is fast. How does mass transport link to gas exchange in insects? The contraction of muscles in the insects can squeeze the trachea which enables mass movements of air in and out. this will speed up gas exchange How do respiratory gases move in and out of the tracheal system? - along a diffusion gradient - mass transport - the ends of the tracheoles fill with water How do respiratory gases move in and out of