biology paper 1

explain how changes in microscope technology, including electron microscopy, have enabled us to see cell structures and organelles with more clarity and detail than in the past and increased our understanding of the role of sub-cellular structures

improvements in microscope technology, especially the invention of the electron microscope, have greatly increased magnification and resolution, allowing scientists to see smaller organelles, such as ribosomes and mitochondria, in much greater detail, we now have a better understanding of how sub-cellular structures function and interact inside cells

recall what an electron microscope is

microscope that uses a beam of electrons instead of light to form an image of a specimen, it provides much higher magnification and resolution than a light microscope

recall what is meant by an instrument’s resolution

resolution is the ability of an instrument, such as a microscope, to distinguish between two points that are close together, the higher the resolution, the clearer and more detailed the image

explain why some cell structures can be seen with an electron microscope but not with a light microscope

an electron microscope has a much higher resolution than a light microscope, this allows it to detect and show very small structures, such as ribosomes or the internal membranes of mitochondria, which are too small to be seen using light

identify the parts of plant and animal cells

nucleus, cytoplasm, cell membrane, mitochondria, ribosomes, cell wall, chloroplasts, vacuole

describe the functions of the nucleus

controls the activities of the cell and contains the genetic material (dna) that determines the cell’s structure and function

describe the functions of the cell membrane in eukaryotic cells

controls the movement of substances into and out of the cell and provides a boundary that separates the cell from its surroundings

describe the functions of the cell wall in eukaryotic cells

the cell wall provides structure and support to the cell, helping it maintain its shape

describe the functions of the chloroplasts

site of photosynthesis in plant cells, they contain chlorophyll, which absorbs light energy to make glucose from carbon dioxide and water

describe the functions of the mitochondria

site of aerobic respiration, where energy is released from glucose to produce atp for the cell’s activities

describe the functions of the ribosomes in eukaryotic cells

sites of protein synthesis, where amino acids are joined together to make proteins according to the instructions in the dna

describe how sperm cells are adapted to their function

flagellum to swim towards the egg, many mitochondria to provide energy for movement, an acrosome containing enzymes to digest the egg’s outer layer, and a haploid nucleus with half the number of chromosomes

describe how egg cells are adapted to their function

large and contain nutrients in the cytoplasm to support the early development of the embryo, they have a haploid nucleus and a membrane that hardens after fertilisation to prevent other sperm from entering

describe how ciliated epithelial cells are adapted to their function

hair-like structures called cilia on their surface move in a coordinated way to move substances, such as mucus, along the surface of tissues like the airways

identify the common parts of bacteria

chromosomal dna, plasmid dna, cell membrane, cell wall, cytoplasm, sometimes flagella

describe the functions of chromosomal dna

contains most of the genetic information needed to control the cell’s activities and replication, it is not contained in a nucleus

describe the functions of plasmid dna

plasmid dna carries extra genes, such as those for antibiotic resistance, which can provide advantages to the bacterium, plasmids can be shared between bacteria

describe the functions of ribosomes in prokaryotic cells

ribosomes in prokaryotic cells are smaller than in eukaryotes and are the site of protein synthesis, where proteins are made for cell growth and repair

describe the functions of flagella

tail-like structures that enable bacteria (and some other cells) to move through liquids, they rotate to propel the cell forward, helping it move towards nutrients or away from harmful substances

describe why bacteria are classified as being prokaryotic

their cells do not have a nucleus or membrane-bound organelles, their genetic material is found as a single circular chromosome in the cytoplasm

examples of enzymes: what is amylase and where is it found in the human body and other species

found in saliva and the small intestine; breaks down starch into sugars

examples of enzymes: what is protease and where is it found in the human body and other species

e.g. pepsin, trypsin, found in the stomach and small intestine; breaks down proteins into amino acids

examples of enzymes: what is lipase and where is it found in the human body and other species

found in the pancreas and small intestine; breaks down lipids into fatty acids and glycerol

recall the subunits from which carbohydrates, proteins and lipids are formed (sugars, amino acids, fatty acids and glycerol)

carbohydrates are made from simple sugars, proteins are made from amino acids, lipids are made from fatty acids and glycerol

describe what enzymes do

catalyse the synthesis and breakdown of substances, such as carbohydrates, proteins and lipids, by speeding up the rate of reaction

define an enzyme

biological catalyst made of protein that speeds up chemical reactions in living organisms without being used up

explain why catalysis by enzymes is important for life processes

enzymes are essential because they allow chemical reactions in cells to occur quickly enough to sustain life, without enzymes, most reactions would be too slow at body temperature

describe how to test for starch in food

add a few drops of iodine solution to the food sample, if starch is present, the iodine changes from brown/orange to blue-black, if starch is absent, it stays brown/orange

describe how to test for reducing sugars in food

add benedict’s solution to the food sample and heat it in a water bath at around 80°c, if reducing sugar is present, the solution changes from blue to green, yellow, orange or brick-red depending on the amount of sugar, if no reducing sugar is present, it remains blue

describe how to test for proteins in food

add biuret reagent (or sodium hydroxide and copper sulfate) to the food sample, if protein is present, the solution changes from blue to purple/lilac, if protein is absent, it stays blue

describe how to test for lipids in food

add ethanol to the food sample and shake it, then add water, if lipid is present, a milky white emulsion forms, if lipid is absent, the solution remains clear

explain how calorimetry can be used to measure the energy in food

measures the energy released from food when it is burned, the food sample is burned under a test tube of water, and the temperature rise of the water is measured

formula to calculate the energy in food

energy (j) = mass of water (g) × temperature rise × 4.2

state what enzyme specificity means

each enzyme only catalyses one particular type of reaction because its active site fits only one specific substrate

state that an enzyme's action is due to its active site

an enzyme’s action is due to its active site, which binds to the substrate and allows the reaction to take place

describe the role of the active site in enzyme function (including specificity)

the region on an enzyme where the substrate binds, its shape is complementary to the substrate, so only that substrate fits, giving the enzyme its specificity

use the lock-and-key model to develop explanations for enzyme activity

in the lock-and-key model, the enzyme’s active site is the “lock,” and the substrate is the “key”, only the correct substrate fits the active site, when they bind, an enzyme–substrate complex forms and the reaction occurs, the products are then released and the enzyme is free to catalyse another reaction

explain why enzymes have a particular shape, as a result of the sequence of amino acids in the chain

enzymes are proteins made from long chains of amino acids, the sequence of amino acids determines how the chain folds into a specific 3d shape, which forms the enzyme’s active site, this shape is essential for the enzyme’s function

explain how enzymes become denatured

enzymes become denatured when high temperatures or extreme ph values cause the shape of their active site to change, the substrate no longer fits, so the enzyme can no longer catalyse the reaction

describe the effect of temperature on enzyme activity

as temperature increases, enzyme activity increases because enzymes and substrate molecules move faster and more collisions occur, however, above the enzyme’s optimum temperature, the active site changes shape (denatures), and the reaction rate rapidly decreases

describe the effect of substrate concentration on enzyme activity

as substrate concentration increases, enzyme activity increases because more substrate molecules can collide with enzyme active sites, the rate levels off when all active sites are occupied — the reaction is then at its maximum rate

describe the effect of ph on enzyme activity

each enzyme has an optimum ph where it works best, if the ph is too high or too low, the active site’s shape changes (denatures), reducing or stopping enzyme activity

explain what is meant by the optimum ph/temperature of an enzyme

the optimum ph or temperature of an enzyme is the condition at which the enzyme works at its fastest rate, at this point, the shape of the active site is perfect for binding to the substrate

outline three ways substances are transported

diffusion, osmosis and active transport

describe how substances are transported by active transport (including the need for energy)

active transport moves substances from a low concentration to a high concentration across a cell membrane, this process requires energy from respiration and uses carrier proteins in the membrane to move molecules against the concentration gradient

explain how substances are transported by diffusion

diffusion is the net movement of particles from an area of high concentration to an area of low concentration, down a concentration gradient, it does not require energy and continues until concentrations are equal

explain how substances are transported by osmosis

osmosis is the diffusion of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration, it does not require energy

explain the effects of osmosis on animal cells and tissues

if too much water enters, the cell may burst (lysis); if too much water leaves, it shrinks (crenation)

explain the effects of osmosis on plant cells and tissues

water entering causes the cell to become turgid; if water leaves, the cell becomes flaccid and may plasmolyse as the cell membrane pulls away from the cell wall

which molecules are produced when a protein is broken down

when a protein is broken down, it is digested into amino acids

how can temperature be controlled when investigating enzyme activity at different ph levels

temperature can be controlled by carrying out the experiment in a water bath or thermostatically controlled environment so that all samples are kept at the same temperature throughout the investigation

safety precaution when using a swab to collect cells inside the mouth to be seen under microscope

use a new, sterile swab for each person to prevent the spread of microorganisms or infection, dispose of the swab safely after use

describe how to use a microscope to view cells at a particular magnification (1)

place the slide on the stage and secure it with clips, select the lowest-power objective lens and use the coarse focus to bring the image roughly into focus, adjust with the fine focus for a clear image

describe how to use a microscope to view cells at a particular magnification (2)

to increase magnification, switch to a higher-power lens and refocus carefully, calculate total magnification by multiplying the eyepiece lens magnification by the objective lens magnification

why do root hair cells not contain chloroplasts

root hair cells do not contain chloroplasts because they are underground and do not receive light, so they cannot carry out photosynthesis, their function is to absorb water and mineral ions, not to make food

how is temperature rise measured in a bomb calorimeter

food is burned in a sealed container surrounded by water, a thermometer or temperature probe measures the temperature rise of the water, which is used to calculate the energy released from the food

how is energy correlated to temperature rise in a bomb calorimeter

the higher the amount of energy, the greater the temperature rise

advantages of using bomb calorimeters (1) reduced heat loss

sample is burned in a sealed chamber to reduce heat loss to the environment

advantages of using bomb calorimeters (2) water

sample chamber is surrounded by another chamber of water in which the temperature change is measured

advantages of using bomb calorimeters (3) reliability

sample is burned in pure oxygen to ensure complete combustion

why does an object rise to the surface of a liquid?

an object rises to the surface of a liquid when its density is less than the density of the liquid, a less dense object will be buoyant and float, while a more dense object will sink

how can a substance’s ph be changed to more acidic?

lipase breaks down lipids in substance into fatty acids and glycerol, the production of fatty acids increased the concentration of hydrogen ions which caused the ph to decrease from 7 to 5

how can a substance’s ph be changed to more alkaline?

urease breaks down urea into ammonia and carbon dioxide, the ammonia reacts with water to form ammonium ions and hydroxide ions, the increase in hydroxide ions reduces the concentration of hydrogen ions, so the ph rises

if ph does not change in a particular mixture what can we assume happened?

denaturation

what are the control variables when investigating effect of ph on enzyme activity?

temperature, enzyme concentration, substrate concentration, volume of solution, time allowed for reaction, type of enzyme and substrate, mixing

suggest improvements that can be made when investigating effect of ph on enzyme activity?

using a wider range of temperatures with smaller intervals or using a water bath instead of a bunsen burner

explain why amylase is not produced in the stomach.

carbohydrase enzymes break disaccharides and polysaccharides into monosaccharides (simple sugars). carbohydrase enzymes are produced in your mouth (in saliva), pancreas and small intestine

relationship between glucose and starch

glucose molecules are joined together to form starch to store energy

why is food mashed before adding enzymes?

mashing increases the surface area of the food, giving enzymes more contact with it and increasing the rate of digestion

why is the same volume of solution used when investigating effect of ph on enzyme activity?

ensures that the concentration of the substrate (lactose) is a controlled variable, allowing for a fair comparison between the different tests, as any change in the rate of reaction can be attributed solely to the change in the number of enzyme beads and not to a change in the amount of substrate available

relationship between mass increase and water potential

a substance with a lower initial water potential will have a greater increase in mass when placed in distilled water

why do calorimeters need a lid?

helps to prevent heat loss to the surroundings by convection and evaporation, ensuring heat change measured is as accurate as possible and accounts for the heat transfer within the system

why do we stir the water in a calorimeter?

ensures that the heat is evenly distributed throughout the water, providing a more accurate and uniform temperature reading

what happens during interphase in the cell cycle?

during this phase, the cell's dna is replicated to create two identical copies of each chromosome. the cell also increases its mass and synthesizes new organelles, such as mitochondria and ribosomes

what happens during prophase in the cell cycle?

the chromosomes condense and become visible, the nuclear membrane breaks down, and the spindle fibres begin to form

what happens during metaphase in the cell cycle?

the chromosomes line up along the equator (middle) of the cell, the spindle fibres attach to the centromeres of the chromosomes

what happens during anaphase in the cell cycle?

the spindle fibres pull the two chromatids of each chromosome apart towards opposite poles of the cell, this separates the replicated chromosomes

what happens during telophase in the cell cycle?

a new nuclear membrane forms around each set of chromosomes at the poles of the cell. the chromosomes uncoil and become long and thin again, this stage marks the end of mitosis

what happens during cytokinesis in the cell cycle?

division of the cytoplasm, results in two separate daughter cells, each with its own nucleus, in animal cells, the cell membrane pinches inward to divide the cytoplasm, while in plant cells, a cell plate forms

describe the division of a cell by mitosis

the production of two daughter cells, each with identical sets of chromosomes in the nucleus to the parent cell, and that this results in the formation of two genetically identical diploid body cells

describe cancer

the result of changes in cells that lead to uncontrolled cell division

why is mitosis important for repair in an organism? (growth)

multicellular organisms grow by increasing the number of cells in their bodies through mitosis

why is mitosis important for repair in an organism? (repair and replacement)

mitosis replaces old, worn-out, or damaged cells, helping to heal injuries and maintain tissue function

why is mitosis important for repair in an organism? (asexual reproduction)

in some organisms, mitosis is the primary method of reproduction, creating new individuals that are genetically identical to the parent

explain why organisms may rely on asexual reproduction (efficiency)

only requires one parent, which means organisms can reproduce without having to find a mate which is helpful in environments where finding a mate is difficult

explain why organisms may rely on asexual reproduction (adaptability)

since the offspring are genetically identical to the parent, they are well-suited to a stable environment where the parent has already proven to be successful

explain why organisms may rely on asexual reproduction (speed)

asexual reproduction can also be very rapid, allowing for a quick increase in population size

describe how mitosis produces genetically identical, diploid cells

interphase, prophase, metaphase, anaphase, telophase, cytokinesis

describe how cancers grow

caused by a mutation in the genes that control cell growth and division causing cells to divide uncontrollably, forming a mass of cells called a tumour, the cells in the tumour can continue to divide and grow, invading surrounding tissues and potentially spreading to other parts of the body through the bloodstream or lymphatic system

define growth in animals

an increase in cell number and size

explain the importance of cell differentiation in the development of specialised cells

this process is where a less specialized cell becomes a more specialized cell type, crucial for the development of multicellular organisms as it allows for the formation of specialized cells with specific structures and functions, which are essential for the proper functioning of tissues, organs, and organ systems

describe how structure of nerve cells is related to their function

long, elongated structure with dendrites and an axon, adapted for their function of transmitting electrical signals (nerve impulses) over long distances, the dendrites receive signals from other neurons, and the axon transmits the signal to the next cell

describe how structure of red blood cells is related to their function

biconcave discs, which increases their surface area to volume ratio, allowing for efficient oxygen absorption, they also lack a nucleus and other organelles, which provides more space for haemoglobin, the protein that binds to and transports oxygen

describe how structure of muscle cells is related to their function

long and contain protein filaments called actin and myosin, these filaments are arranged in a way that allows them to slide past each other, causing the muscle cell to contract, this contraction is the basis of all muscle movement

describe how structure of sperm cells is related to their function

sperm cells have a streamlined head containing the nucleus with genetic material, a midpiece packed with mitochondria for energy, and a long tail (flagellum), an adaptation for their function of swimming towards and fertilizing an egg providing motility, and the mitochondria provide the energy for this movement

describe how structure of egg cells is related to their function

large and spherical, containing a large amount of cytoplasm and nutrients, this structure is related to their function of providing nourishment and a suitable environment for a developing embryo after fertilization

describe how structure of white blood cells is related to their function

irregular in shape and can change their form, this allows them to move through the walls of blood vessels and into tissues to fight infections, they also contain a nucleus and other organelles that are necessary for their function of identifying and destroying pathogens

stages of growth in plants: describe cell division

the process by which a parent cell divides into two or more daughter cells, in plants, this occurs primarily in the meristematic tissues, such as the root and shoot tips, leading to an increase in the number of cells and contributing to the plant's overall growth

stages of growth in plants: describe cell elongation

the process where newly formed cells in the meristematic regions expand in size, crucial for plant growth, as it is responsible for the majority of the increase in the length of the stem and roots, involving the uptake of water, which increases the turgor pressure inside the cell, causing the cell wall to stretch and expand

stages of growth in plants: describe cell differentiation

the process where cells change from a simple, unspecialized state to a more specialized state, during this stage, elongated cells develop specific structures and functions, forming different types of tissues, allowing the plant to perform various functions necessary for its survival