science

microscopes

electron microscope uses a beam of electrons instead of light to create an image, providing higher resolution and magnification than a light microscope

some cell structures be seen with an electron microscope but not a light microscope as electron microscopes have a much higher resolution than light microscopes, shorter wavelength of electrons allow for greater detail so smaller structures are visible

total magnification = magnification of eyepiece lens x magnification of objective lens

size calculation for using magnification: actual size = image size/measured size

the SI prefixes are: milli = 0.001, micro = 0.000001, nano = 0.000000001, pico = 0.000000000001

resolution

ability of an instrument to distinguish between two points that are close together

compare animal and plant cells in terms of structures

both animal and plant cells contain: nucleus which contains genetic material and controls cell activities, cell membrane which controls movement of substances in and out of the cell, cytoplasm where chemical reactions take place, mitochondria which is the site of aerobic respiration and releases energy and ribosomes which are the site of protein synthesis

only plant cells contain: the cell wall which provides structure and support, chloroplast which contains chlorophyll for photosynthesis and the permanent vacuole which rids of waste products

estimating sizes

when using the microscopes field of view: measure the diameter of the field of view, estimate how many cells fit across and divide diameter by number of cells

when using scale bars: actual size = measured size/scale bar length

sperm cell adaptations

flagellum enables movement towards the egg, many mitochondria provides energy for movement, acrosome contains enzymes to digest the egg’s outer layer, haploid nucleus contains half the genetic material for fertilisation

egg cell adaptations

nutrient rich cytoplasm provides energy for embryo development, haploid nucleus ensures correct chromosomes number after fertilisation, cell membrane changes after fertilisation preventing multiple sperm from entering

ciliated epithelial cell adaptations

cilia moves substances like mucus in airways or egg in oviduct
mitochondria provides energy for cilia movement

cell functions

presence of many mitochondria means it requires a lot of energy e.g muscle or sperm cell, specialized structures like cilia for flagellum indicate movement function, large surface areas indicate absorption or exchange function e.g root hair cell, enzymes or storage of nutrients indicates digestion or energy storage function e,g acrosome in sperm or egg in oviduct

parts of bacteria

chromosomal DNA which contains genetic material and controls cell activities, plasmid DNA which provides extra genes e.g for antibiotic resistance, cell membrane, cell wall not made of cellulose, cytoplasm and flagellum in some

compare eukaryotic and prokaryotic cells

eukaryotic cells have a present nucleus, larger size, contain membrane bound organelles, linear chromosomes for DNA, cell wall only in plant cells

prokaryotic cells have an absent nucleus as DNA is free in cytoplasm, smaller size, no membrane bound organelles, circular chromosomal DNA + plasmids, cell wall present in all

where are enzymes found?

in amylase enzymes are found in saliva and pancreas, breaks down starch into maltose, in protease enzymes are found in the stomach (pepsin) and pancreas, breaks down proteins into amino acids, in lipase enzymes are found in the pancreas and small intestine, breaks down lipids into fatty acids and glycerol

carbohydrates are made up of sugars such as glucose

enzymes

enzymes are biological catalysts that speed up chemical reactions without being used up, they catalyse reactions by speeding the breakdown or synthesis of molecules

they are important for speeding up life processes such as respiration and digestion and without enzymes reactions would be too slow to sustain life

enzymes have a particular shape as they are proteins made of amino acids linked in a specific sequences: this determines how the protein folds, forming a specific 3D shape with a unique active site

enzyme specificity

each enzyme only catalyses one specific reaction as its active site is a specific shape that fits only one substrate

the active site

has a specific shape that only fits one substrate to ensure only one type of reaction takes place, after the reaction, the enzyme remains unchanged and can be reused

enzyme action is due to active site which binds to the substrate allowing the reaction to occur

lock and key model explanation

the substrate fits into the enzymes active site, the reaction occurs breaking down or building molecules, the products are released and the enzyme remains unchanged

how do enzymes become denatured

high temperatures break bonds, changing the enzymes shape
extreme pH alters the active site structure
a denatured enzyme no longer fits the substrate, stopping its function

effect of temperature on enzyme activity

as temperature increases, enzyme activity increases due to more kinetic energy and more frequent collisions

at the optimum temperature the enzyme works fastest, above the optimum, the enzyme denatures as bonds breaks, changing the active site shape

temperature affects enzyme activity as it affects kinetic energy, collision frequency and denaturation

effect of substrate concentration on enzyme activity

increasing substrate concentration increases enzyme activity as more collisions occur, maximum rate is reached when all enzyme active sites are occupied

substrate concentration affects enzyme activity as affects the frequency of enzyme-substrate collisions

effect of pH on enzyme activity

each enzyme has an optimum pH which it works best, too high or too low pH alters the enzyme shape, changing the active site and denaturing the enzyme

pH affects enzyme activity as it affects bonding within the enzyme, changing the active site and denaturing if too extreme

rate of enzyme activity

rate = amount of product formed or substrate used/time taken

how are substances transported

diffusion: the passive moment of particles from a high to low concentration where no energy is required, osmosis: diffusion of water across a partially permeable membrane where water moves from a high water potential to a low water potential and no energy is required, active transport: moves substances against the concentration gradient from a low to high concentration, requires energy for respiration and uses carrier proteins in the cell membrane

effect of osmosis on cells and tissues

in animal cells when water enters the cell swells and may burst (lysis) and when water leaves the cell shrinks (crenation)

in plant cells when water enters cell becomes turgid (firm) and when water leaves cell becomes flaccid; sever loss causes plasmolysis

osmosis investigation in potatoes

cut equal sized potato pieces
weigh, place in different sucrose solutions and leave for a set time
remove, dry and reweigh
calculate percentage mass change: final mass - initial mass/initial mass x 100

cell cycle

during interphase the cell grows, DNA is replicated and organelles are copied, during mitosis the chromosomes condense, nuclear membrane breaks down and spindle fibres form, chromosomes align at the equator of the cell, chromatids separate and are pulled to opposite poles, new nuclear membranes form around each set of chromosomes, during cytokinesis the cytoplasm divides, forming two genetically identical daughter cells

why is mitosis important

growth increases the number of cells in an organism
repair to replace damaged or dead cells
asexual reproduction produces genetically identical offspring

why do organisms rely on asexual reproduction

fast reproduction
no need for a mate so beneficial in stable environments
genetically identical offspring ensures successful traits are passed on

how does mitosis produce genetically identical diploid cells

DNA is copied during interphase, sister chromatids separate during mitosis
two genetically identical diploid daughter cells are formed, each with two sets of chromosomes

how do cancers grow

cancer is uncontrolled cell division due to mutations in genes controlling the cell cycle, tumours form when abnormal cells divide rapidly. cancer cells ignore signals to stop dividing and do not undergo normal cell death

what is growth in animals

an increase in cell number by mitosis and cell size

importance of cell differentiation

allows cells to become specialised for different functions
essential for growth, repair and development
enables complex organisms to function efficiently

stages of growth in plants: cell division

cell division where cell divides by mitosis to produce new cells

cell elongation where new cells increase in size causing plants to grow

cell differential where cells develop into specialised cells taking on specific functions

importance of cell differentiation in plants

allows cells to become specialised for specific roles, essential for efficient plant function
enables the plant to perform complex processes such as photosynthesis, water transport and nutrient absorption

structure and functions of specialised cells

muscle cells are long and contain mitochondria for contraction

nerve cells have long axon for fast electrical signals, myelin sheath for insulation

red blood cells have no nucleus for more oxygen and biconcave shape for larger surface area

root hair cells are long, thin projection to increase surface area for water and mineral absorption

xylem cells hollow tubes with thick walls for the transport of water and minerals

phloem cells have sieve plates for transporting sugars and companion cells for metabolic support

palisade methyl cells are packed with chlorophyll for photosynthesis

stem cells in animals and plants

animals: found embryos, bone marrow and other tissues, can differentiate into various types of cells, allowing for growth, repair and replacement of damaged cells

plants: found in meristematic tissues such as the root and shoot tips, stem cells in meristems allow for growth and the production of new tissues such as leaves and flowers

what is the difference between embryonic and adult stem cells

embryonic stem cells are pluripotent, can differentiate into any time of cell in the body whereas adult stem cells are multipotent and can only differentiate into a limited range of cell types

stem cells in medicine

blood disorders are treated using bone marrow stem cells to treat leukaemia, regenerative medicine where stem cells regenerate damaged tissues e.g spinal cord injury and heart disease, growing new tissues for organ transplants

benefits including treating incurable diseases, regenerating damaged tissues and restoring function and risks include tumour formation if stem cells grow uncontrollably, rejection by the immune system if not properly matched, ethical concerns about using embryonic stem cells

general conclusion of using stem cells in medicine

the benefits may outweigh the risks, but careful regulation and further research are needed to ensure safe and ethical use

difference between CNS and PNS

the central nervous system includes the brain and spinal cord

the peripheral nervous system includes sensory neurons and motor neurons that connect the CNS to the rest of the body

how does the nervous system detect stimuli

sensory receptors detect stimuli
sensory neurones transmit the electrical impulses from receptors to the CNS for processing

structure of sensory neurones (1)

cell body located near the spinal cord, dendrites receive signals from receptors, axon carries the electrical impulse towards the CNS, myelin sheath insulates the axon speeding up impulse transmission,

routes that impulses take to and from the brain

sensory neurones carry impulses from receptors to the CNS, motor neurones carry impulses from the CNS to effectors (muscles or glands), relay neurones transmit signals within the CNS

how are sensory neurones adapted to their function

myelin sheath acts as an insulator, speeding up the transmission of electrical impulses

allows impulses to travel over long relay neurones transmit signals within the CNS to the CNS

dendrites increases surface area to receive signals from sensory receptors

how does the nervous system respond to stimuli

sensory receptors detect a stimulus and send an electrical impulse through sensory neurones to the CNS,

CNS processes information and sends a response via motor neurones to an effector which carries out the response

structure of motor neurones

cell body located in the CNS
axon carries impulses from CNS to effectors
dendrites receive signals from relay neurones

structure of relay neurones

found in the CNS
short axon and dendrites connect sensory neurones to motor neurones

how are motor neurones adapted to their function (long axon)

long axon carries impulses over long distances to effectors

myelin sheath insulates the axon increasing the speed of electrical impulse transmission

dendrites receives signals from relay neurones

what is a synapse

synapse is a junction between two neurones

electrical impulse reaches the end of one neurone and triggers the release of neurotransmitters which diffuse across the synapse to bind with receptors on the next neurone, allows impulses to travel over long relay neurones transmit signals within the CNS to the CNS

how does the structure of the reflex arc allow for faster response

the reflex arc bypasses the brain, allowing for a faster response to protect the body from harm

sensory neurones transmit the signal to the spinal cord where it is relayed to the motor neurones causing an immediate response to the effector

structure and function of the reflex arc

stimulus is detected by sensory receptors, sensory neurone transmits impulse to spinal cord, relay neurone passes the signal to the motor

the motor neurone carries the impulse to the effector causing a response
no involvement of the brain allows a quicker response

how are gametes produced

meiosis: the process that produces haploid gametes from a diploid cell, two divisions are made reducing the chromosome number by half, producing four genetically diverse haploid gametes

why haploid gametes are needed for sexual reproduction

haploid gametes contain half the chromosome number
when fertilisation occurs, the fusion of two haploid gametes restores the diploid chromosome number ensuring the offspring has correct number of chromosomes

what is an organism’s genome

complete set of genetic material in its cells, including all the genes

genes

found on chromosomes, allocated in the nucleus of cells

carry instructions for building and maintaining an organism, determining characteristics like eye colour and susceptibility to disease

where is DNA found in a eukaryotic cell

nucleus and in small amounts of mitochondria

bases in DNA

adenine (A) and thymine (T)
cytosine (C) and guanine (G)

DNA

strands held together by hydrogen bonds between the paired bases forming the double helix structure

double helix structure consisting of two complementary strands twisted around eachother, sugar phosphate backbone on the outside and the base pairs in the middle

how DNA can be extracted from fruit

mash the fruit to break open the cells
add salt solution to break down the cell membrane and release DNA

add detergent to dissolve the cell membrane and nuclear membrane
add alcohol to precipitate the DNA which appears as a white, stringy substance

difference between a gene and an allele

a gene is a section of DNA that codes for a particular protein, determining a specific trait
an allele is a variant form of a gene which can result in different expressions of a trait

effects of alleles on inherited characteristics

different alleles of a gene produce variations in the phenotype of an organism, influencing characteristics like eye colour or blood type

relationship between genotype and phenotype

genotype is the genetic makeup of an organism
phenotype is the observable expression of these genes

homozygous and heterozygous genotypes

homozygous means both alleles are the same
heterozygous means alleles are different

punnet square

used to show to possible combinations of alleles from both parents, indicating the likelihood of offspring inheriting certain traits

why may the effects of some alleles not been seen in the phenotype

some alleles are recessive and only expressed in the phenotype when two recessive alleles are present
if a dominant allele is present the recessive allele effects are masked in the phenotype

how is sex determined in humans
(by combination of sex chromosomes)

a female can only pass on a X chromosome while a male can pass on either an X or Y chromosome, determining the sex of the offspring

examples of characteristics controlled by multiple genes

height, skin colour and eye colour are all examples which interact to produce a wide range of phenotypic outcomes

mutation

change in DNA sequence of a gene which may alter the structure of the protein it codes for

causes variation by changing the protein produced by a gene, this altered protein may not function properly or it may affect a biological process which the protein is involved in leading to a changed phenotype

potential applications of mapping human genomes

can help identify genes linked to diseases
assist in diagnosing genetic disorders
inform the development of targeted treatments and personalised medicine

how can mutation cause a variation

mutation changes the protein produced by a gene, this altered protein may not function properly or it may affect a biological process which the protein is involved in leading to a changed phenotype

examples of mutations in human genes

sickle cell is caused by a mutation in the haemoglobin gene, which affects red blood cells and leads to a distorted shape

cystic fibrosis is caused by mutations in the CFTR gene affecting the lungs and digestive system

silent mutations have little to no obvious effect on the phenotype as they do not change the amino acid sequence of the protein or do not affect protein function

why may mutations have no effect on the phenotype

many mutations occur in non coding regions of the DNA or result in silent mutations leading to no observable effect on the phenotype

types of variation

genetic variation iscaused by differences in the genetic material inherited from parents, leading to differences in characteristics

environmental variation is caused by difference in the environment in which an organism lives, which can affect characteristics

continuous variation refers to traits that show a range of values, often influenced by multiple genes and the environment

discontinuous variation refers to traits that have distinct categories or groups often determined by a single gene

causes of genetic variation

mutation changes in the DNA sequence that can create new alleles

sexual reproduction the random combination of alleles from both parents during fertilisation leads to genetically unique offspring

differences in environment factors like temperature, light and nutrition can affect characteristics

acquired characteristics traits developed during an organisms life due to environmental factors like muscle growth from exercise

contribution of genes and environment to variation

genes provide the blueprint for inherited traits, determining many characteristics

environment influences traits like height, weight and skin colour, but does not change genetic code

both genes and environment interact to change the overall variation of characteristics

evolution

gradual change in the characteristics of a species over successive generations due to genetic variation and natural selection

binomial species names

consist of two parts: the genus name and species name
e.g homo sapiens

use examples to explain how evidence support current ideas about human evolution

fossils show physical changes in species overtime, indicating gradual adaptation

stone tools provide insight into early human behaviour, cognitive abilities and technological development, supporting the theory of human evolution by showing advances in tool complexity linked to brain development

examining the age of the rock layers in which they are found using techniques like relative dating or radiometric dating
this estimates their age based on the surrounding fossils or geological features

describe how stone tools created by human like species has developed overtime

stone tools have become increasingly more complex over time
early tools like simple flakes were used for cutting while later tools like hand axes showed improved shaping techniques

this indicates more advanced cognitive skills and social cooperation in human like species

describe the fossil evidence for human species across different years

4.4 million years ago: Ardipithecus ramidus: showing evidence of bipedalism and arboreal adaptation

3.2 million years ago: Australopithecus afarensis: (Lucy) with evidence of upright walking and tool use

1.6 million years ago: Homo erectus: showing larger brain size, evidence of fire use and more sophisticated tools

cause of genetic variation

caused by mutations, meiosis and sexual reproduction

describe how adaptations allow organisms to survive

adaptations are characteristics that increase an organisms chances of survival and reproduction in its environment

examples of this include: camouflage, specialised feeding structures or resistance to disease

explain how natural selection allows some members of a species to survive better than others when conditions change

favours individuals with traits that provide an advantage in changing conditions allowing them to survive and reproduce, passing these beneficial traits to future generations

explain how natural selection can lead to the evolution of a new species

if a population is divided and isolated, different environmental pressures can lead to genetic changes over time
if these changes are significant enough, individuals from different groups may not be able to interbreed - leading to formation of a new species

explain how the development of resistance in organisms supports Darwin’s theory

shows individuals with resistant traits survive and reproduce, passing these traits on to offspring leading to a population with greater resistance over generations

describe how organisms are classified into smaller and smaller groups

based on shared characteristics starting from broadest (domain) to most specific (species)

domain, kingdom, phylum, class, order, family, genus and species

what are the five kingdoms for organisms

Monera (bacteria)
Protista (single celled organisms)
fungi (mushroom and moulds)
plantae (plants)
animalia (animals)

genetic analysis

involves examining DNA sequences to identify similarities and differences between organisms, providing insight into their evolutionary relationships

explain why biologists often now classify organisms into three domains

biologists classify organisms into three domains bacteria, archaea and eukarya - based on genetic differences

this system reflects the deep evolutionary splits between these groups, with differences in their ribosomal RNA sequences indicating fundamental biological distinctions

describe why new breeds and varieties are created

new breeds and varieties are created to enhance desired traits such such as improved yield, diseased resistance or specific characteristics
this is to meet human needs or environmental challenges

what is a genetically modified organism

organism whose genetic material has been altered through genetic engineering techniques to introduce desirable traits such as pest resistance or improved nutritional content

how is selective breeding carried out

involves choosing parent organisms with desirable traits and breeding them to produce offspring with these traits
this is repeated over several generations to enhanced desired characteristics in the population

explain the impact of selective breeding on domesticated plants and animals

can lead to improved traits in domesticated plants and animals such as higher yields, better disease resistance and specific physical traits

can result in reduced genetic diversity, making populations more vulnerable to diseases and environmental changes

stages of genetic engineering

identify the gene of interest in an organism
extract the gene using enzymes
insert the gene into the DNA of a target organisms using vectors

introduce the modified DNA into the target organism’s cells
grow the modified organisms and select those that express the desired trait

recall some uses of selectively bred organisms in agriculture

produce crops with higher yields
animals with improved meat or milk production
plants resistant to pests and diseases
e.g drought resistant crops and disease resistant livestock

uses of genetically engineered organisms

in agriculture crops like Bt corn (resistant to pests) and Golden Rice (enhanced with vitamin A)

in medicine production of insulin, growth hormones and vaccines in genetically modified bacteria

benefits and risks of selective breeding

benefits are improved traits such as higher yields, disease resistance and desirable physical traits

risks are reduced genetic diversity leading to susceptibility to diseases and environmental changes

benefits and risks of genetic engineering

benefits are rapid introduction of specific traits, such as pest resistance or enhanced nutritional content with precise control over genetic changes

risks are unintended effects on the organism or the environment, ethical concerns about modifying organisms and potential risks to biodiversity

health

state of complete physical, mental and social well being, not merely the absence of disease or infirmity

disease

condition that negatively affects the normal functioning of the body or mind, often caused by infection, genetic factors or environmental influence

difference between communicable and non communicable dieases

communicable diseases are caused by pathogens like bacteria and viruses and can be spread from person to person

non communicable diseases including heart disease, type 2 diabetes, cancer, stroke and chronic respiratory diseases are not spread between individuals and typically caused by genetic factors, lifestyle choices or environmental factors

what is the role of the immune system in protecting against disease

identifies and attacks pathogens using white blood cells, includes barriers, immune responses and memory cells to recognise and fight previously encountered pathogens