igcse edexcel biology revision (full syllabus)

4 differences between transcription and translation

transcription:

- occurs in nucleus

- produces mRNA

- starts with DNA

- doesn't use tRNA

translation:

- occurs in ribosome

- produces protein

- starts with mRNA

- uses tRNA

How evolution occur by natural selection

1) mutation occurs

2) leads to variation

3) survive better

4) reproduce more

5) pass on alleles to their offspring

Describe the process of animal cloning

- Isolate nucleus from body cell and insert into enucleated egg cell

- Apply electric shock to stimulate cell division by mitosis

- to form embryo

- Embryo transferred into uterus of surrogate mother (to complete its development)

What is dominant allele and recessive allele

dominant allele- Version of gene that only needs one copy to be expressed in phenotype

recessive allele- Version of gene only expressed in homozygous

Describe the structure of DNA molecule

- Double helix

- complementary base pairs

- adenine and thymine, guanine and cytosine

how fermenter is used to grow yeast or bacteria cells (mentioning the suitable conditions)

- Optimum pH: provide optimum pH for enzyme activity.

It is maintained/controlled by using pH probe.

- Nutrients: provide nutrients such as glucose for respiration

-Oxygenation: provide air supply for sufficient o2 for aerobic respiration

- Agitation: stirring paddles to evenly distribute heat, oxygen and nutrients

- Aseptic precautions: fermenter cleaned by steam to kill microorganisms (air filter to prevent contamination)

- Optimum temperature: water jacket to maintain optimum temperature for enzyme activity

Describe the process of micropropagation to clone plants

- collect explant from the plant

- Place explant in sterilized agar nutrient medium containing

- glucose, amino acids and plant hormone

-callus forms

- control light and humidity levels

Describe the process of protein synthesis(transcription and translation)

- transcription occurs in nucleus

- part of DNA unzips

-free nucleotides form complementary base sequence with DNA template strand to form mRNA

- mRNA exits nucleus, enters cytoplasm and attaches to ribosome

-translation occurs in ribosome

- tRNA carries specific amino acids to ribosome

- mRNA codon bind to tRNA anti codon

-thus amino acid chain produced

Advantages of Micropropagation

-quick process

- can be done anytime of year

- produces large number of plants

- produces genetically identical offspring

Describe the process of making yoghurt from milk

- pasteurize the milk

- to kill bacteria

- cool the milk

- add lactobacillus bacteria, it ferments lactose into lactic acid

- this thickens the milk forming yoghurt

Describe the process of selective breeding(E.g.-chicken with no feather)

- Select chickens with no feathers and breed them together

- Select off springs with no feathers and breed them together

- Repeat this process for many generations

how and why fermenter sterilized

with hot steam under high pressure, to prevent contamination.

why yeast cell number decreases near end of process of production of bear.

-less glucose for respiration as it gets used up

- increase in ethanol concentration, which kills yeast

Describe how large amounts of human insulin can be manufactured from genetically modified

- Locate human insulin producing gene and cut using restriction enzyme, leaving it with sticky ends

- use same restriction enzyme to cut bacterial plasmid, leaving it with corresponding sticky ends

- Join cut plasmid and cut gene together with the help of ligase enzyme

- Insert recombinant plasmid back into the bacteria

-place bacteria in fermenter

Describe how a mutation in DNA of a cell can affect the functioning of an enzyme

- a change in the base sequence of template strand occurs

- so mRNA codes for different codon

- different amino acid joins together to form different protein

- thus a different shaped enzyme is produced

give example of mutagens

Ultraviolet rays

define polygenic inheritance

when a characteristic is controlled by lots of genes

Define codominance

when neither allele being dominant to the other, so both are expressed in phenotype

describe causes of genetic variation in offspring

- random mating and random fertilizations

- the environment

- mutation

Define the term transgenic

transfer of genetic material from one species to a different species

Difference between mitosis and meiosis

no. of chromosomes in original cell

no. of daughter cells produced

no. of chromosomes in each daughter cell

meiosis:

number of chromosomes in original cell: 46

number of daughter cells produced: 4

no. of chromosomes in each daughter cell: 23

mitosis:

number of chromosomes in original cell: 46

number of daughter cells produced: 2

no. of chromosomes in each daughter cell: 46

examples of mitosis

.- mitosis occurs during growth and repair.

- cloning and asexual reproduction.

function of:

nucleus

cytoplasm

cell membrane

mitochondria

ribosome

cell wall

permanent vacuole

nucleus : contains genetic material

cytoplasm : site of chemical reactions, contains organelles and enzymes

cell membrane: controls what enters and leaves cell

mitochondria: site of aerobic respiration, providing cell with energy ('powerhouse of cell')

Ribosome- site of protein synthesis (transcription)

cell wall: provides cell support (made from cellulose)

permanent vacuole- contains cell sap

plant vs animal cell diagram

Define:

organelle

cell

organelle: a specialized structure found inside cells that carry out specific functions

cell: the basic functional and structural unit of life

define tissue

tissue: group of similar cells working together to perform a specific function

Surface area to volume ratio

- As an organism gets larger, SA:V ratio decreases (more increase in V, less increase in SA)

- so small organism = LARGE SA:V ratio

- small organisms like bacteria can rely on diffusion for exchange due to LARGE SA:V ratio.

- big organism = SMALL SA:V ratio

- for big organisms diffusion would be too slow due to SMALL SA:V ratio, so they have transport systems.

P.S - disadvantage of large SA:V --> more heat loss.

- so smaller organisms lose more heat, due to large SA:V

how fungi obtain food by saprotrophic nutrition?

- secretes digestive enzymes onto food

- for extracellular digestion

- then absorb the digested food

difference between eukaryotic organisms and prokaryotic organism

Eukaryotes: [yeast, plant, animal]

- has nucleus

- has organelles like mitochondria

- no plasmid

(can be unicellular or multicellular)

Prokaryotes: [bacteria]

- no nucleus

- no organelles

- plasmid present

(always unicellular)

define organ

define organ system

group of tissues working together to perform specific functions

group of organs working together to perform specific function

Define enzyme. How do enzymes work?

- Enzymes are biological catalysts

- that speeds up a reaction, without being used up

-each enzyme has a specific active site that fits a specific substrate like a lock and key

- when an enzyme and its substrate collide, an enzyme-substrate complex forms

effect of temperature and pH in enzyme activity

1) temperature:

- Increase in temp, increases enzyme activity/rate of reaction

- as K.E increases, more collision occurs (more es complex)

- above optimum temp, enzymes will denature, active site shape is altered

- so substrate no longer fit to active site, so rate of reaction decreases

-Decrease in temp decreases rate of reaction as enzymes are inactive(less K.E) (less collision)

- less ES complex formed

2) pH:

- pH above or below the optimum pH decreases enzyme activity

- if change in pH too large, enzyme denature

define antibiotic

Give an example.

medicines that kill bacteria.

e.g: penicillin

how is carbohydrate stored in fungi.

draw yeast cell ( yeast cell is unicellular btw)

- carb is stored as glycogen in fungi

[fungi have cell wall made of chitin ]

draw bacteria diagram

protist vs bacteria

protist:

- nucleus present

- some got chloroplast

bacteria:

- nucleus absent

- no chloroplast

both can have flagellum

Give example of virus and its effect, in humans and plants.

Human: HIV, causes AIDS. (weaken immune system)

plants: tobacco mosaic virus, prevents formation of chloroplasts.

give example of a pathogenic protist and the disease it causes.

pathogenic protist: plasmodium

disease: malaria

Define partially permeable membrane

A membrane that only allows small molecules to pass through and does not let large molecules to pass through.

Features of virus

why are viruses not considered as living organisms?

virus:

- protein coat

- DNA

- they cannot reproduce without a host

- do not feed, respire or move etc.

adaption to function of vein

- valves, to prevent backflow of blood

- wide lumen, to carry large volume of blood

- thin walls, as they carry blood in low pressure

adaptation to function of artery

- elastic tissue, to maintain high BP

- narrow lumen, to maintain high BP

- strong muscle tissue, to withstand high pressure

- thick walls, as they carry blood in high pressure

adaptation to function of capillary

-capillary have walls that are one cell thick, so short diffusion distance for gas exchange

- small, so can fit between cells

- large number of capillaries, increases SA so faster diffusion

- carry blood at low pressure, so slow blood flow, allowing

efficient diffusion

(carries both oxygenated and deoxygenated blood)

suggest why sprint athletes who run only for 10 seconds gain no advantage from having more RBC

- because they run for very short time

- so body does anaerobic respiration

- so no oxygen is needed

function of semi lunar valves

- prevents backflow of blood

- from arteries into ventricles

Explain how coronary heart disease can cause death

- in CHD, coronary artery is blocked

- fat deposits which leads to blood clot

- less blood goes to heart

- so less o2 to muscles

- less aerobic respiration occurs in muscles

- so more anaerobic respiration occurs, producing lactic acid

- which can lead to heart attack and death

factors that may increase the risk of developing coronary heart disease

- genes

- diet (high levels of cholesterol & saturated fat increases chance)

- High blood pressure

- smoking (forms blood clots)

- stress

- age

- Lack of exercise

Suggest 3 reasons why scientists obtain blood samples from a vein rather than from an artery.

1) veins have thinner walls (makes it easier to insert needle)

2) lower pressure (so blood doesn't spit out)

3) wider lumen

phagocyte and lymphocyte diagram

phagocyte:

- lobed nucleus

- cell membrane

-cytoplasm

lymphocyte:

- round nucleus

- cell membrane

- cytoplasm

function of:

capillary

artery

vein

Capillary: Absorbs glucose and amino acids (villi), allows gas exchange(alveoli) and removes waste products(co2 and urea) from blood.

Artery: carries blood away from the heart (usually O)

Vein: Carries blood towards the heart (usually DO)

[artery always carry blood away from heart]

[vein always carry blood towards heart]

role of platelets in blood clotting.

Platelet function and structure

- platelets clot the blood at site of wound

- by producing chemicals that causes soluble fibrinogen, to form mesh of insoluble fibrin

function:

-prevents blood loss & entry of microorganisms

Structure: small fragments of cell, no nucleus

(formed in bone marrow)

RBC and WBC differences

RBC: (erythrocyte)

- Biconcave shape, no nucleus, contain hemoglobin.

- smaller in size

- RBC function is to transport oxygen around body

- produced in red bone marrow of short bone (ex: ribs)

WBC: (leukocyte)

- Irregular shape, has nucleus, no hemoglobin

- larger in size

- WBC function is to protect body against diseases.

- produced in the white bone marrow of long bone (ex: legs)

Fish farming

- use nets to prevent predation

- provide fish the food with high protein to give more growth

- use pumps to maintain optimum oxygen levels

- Remove waste such as faeces from water

- use antibiotics to reduce disease

- use selective breeding to maximise yield

suggest why athletes have lower resting heart rate (4marks)

- athletes have trained a lot

- so they have stronger heart

- so they can pump more blood in each beat

- and hence provide more o2

what is plasma. State its composition and function

Plasma: liquid part of blood, it is yellowish in color

Composition:

water

nutrients (amino acids and glucose)

waste products ( urea, CO2)

hormones, enzymes, antibodies and vitamins

Function:

- carries blood cells, dissolved nutrients and waste products around body

- distributes heat around body

Explain difference in concentration of gases in blood leaving fish and human heart (4marks)

- blood leaving fish heart has less o2 and more co2

- because it has single circulation

-blood leaving human heart has more o2 and less co2

- because blood gets oxygenated in lungs

- and co2 is removed

Sometimes baby has hole in septum.

Suggest the effects that this condition may have on baby.

- allows O and DO blood to mix

- so less oxygen may to transported to body

- less respiration and less energy

- so baby may have less growth

Describe how WBC is used by body to defend against infection/disease

-WBC has phagocytes who destroy pathogens by process of phagocytosis

- where enzymes will digest pathogen

- WBC also has lymphocytes who recognizes antigens and produces specific antibodies.

- The antibodies clump the pathogens together and destroy them

- Lymphocytes also produce memory cells so that next time pathogen attacks, antibodies are released faster.

function of atria in the body

- pump blood into ventricles

- receive DO blood from vena cava

- receives O blood from pulmonary vein

explain what the term immune response means

-it is a response to antigens of pathogens by WBC

- where they produce antibodies

How does vaccination protect body from disease?

- weakened pathogens are injected to body

- Lymphocytes recognize the antigens and produce specific antibodies

- memory cells are made

- so when normal pathogen enters body, antibodies are released faster

blood in pulmonary artery vs aorta

- In P.A (pulmonary artery) blood travels in lower pressure but aorta higher pressure

- P.A carries DO blood, but aorta O blood

- P.A carries blood that has higher CO2 conc.

Describe the test for presence of:

glucose(or reducing sugar)

proteins

Test for glucose:

- heat sample with water bath

- add Benedict solution

- brick-red if glucose present

Test for protein:

- Add biuret solution

- purple if protein present

Describe the test for presence of:

starch (or non reducing sugar)

lipids(or fat)

Test for starch:

- Add iodine solution

- orange-brown solution turn blue-black if starch present

Test for lipids:

- Add ethanol and water

- cloudy emulsion forms if lipid present

what is a balanced diet

In which places are proteins, lipids and carbohydrates digested?

- A diet containing protein, carbohydrates, lipids, fibre, mineral ions, vitamin and water

- in the right amount and right proportion

- Proteins: stomach and small intestine

- Lipids: small intestine

- Carbohydrates- Mouth and small intestine

Source, function and deficiency disease of:

Calcium

Iron

Calcium:

- milk

- strengthen bones and teeth

- rickets

Iron:

- Red meat

-helps in formation of hemoglobin(which transports o2 around blood for respiration)

- anemia

Name structures of human alimentary canal

where is bile made, then stored and then released into?

- Bile is made in the liver, then stored in gall bladder and then finally released into small intestine (where it helps to digest lipids)

Source, function and deficiency disease of:

vitamin-A

vitamin-C

vitamin-D

Fibre

vitamin-A:

- Butter and carrot

- For healthy vision in low light and healthy skin

- Night blindness

Vitamin-C:

- Citrus fruits such as lemon and orange.

- Helps to absorb iron

- scurvy

vitamin-D:

- sunlight

- Helps to absorb calcium (strong bones)

- Rickets (same as calcium as it helps absorb calcium)

Fibre:

- vegetables

-makes the bulk of undigested food to keep it moving through gut

- constipation

Role of digestive enzymes in digestion

Amylase

maltase

protease

lipase

Amylase: digests starch into maltose

Maltase: maltose ---> glucose

Protease: protein ---> amino acids

Lipase: Lipids ----> fatty acids and glycerol

Structure and adaption of small intestine and villus absorbing food

- Small intestine is long and folded, more SA.

- Contains lots of villi and microvilli, increases SA for absorption

-wall of villi one cell thick, short diffusion distance

- Contains lots of capillaries ,to maintain concentration gradient and absorb glucose & amino acids.

- Lacteals present, to absorb fats

Investigate energy content in food sample (comparing 2 foods' energy)

1) Take same mass of water

2) Measure mass of food

3) Burn food under boiling tube of water

4) Measure increase in temperature of water

5) use the equation to calculate energy content:

Energy content = mass of water(g) x 4.2 x temperature change

[6) the food that gave highest temperature rise has most energy]

Explain what happens to protein in stomach

1) Protein mechanically digested by churning

2)Stomach secretes HCL which provides optimum pH for enzyme activity.

3) pepsin digests protein into polypeptides

[polypeptide later digested into amino acids in small intestine by protease]

​

student uses 2 methods to investigate energy content of food.

method A apparatus:

- water

- thermometer

- food burning out open

method B apparatus:

-coiled copper pipe

-thermometer

- stirrer

-insulation

-lid

- food burning inside

- oxygen supply

Explain why method B produces more accurate results than method A.

- copper pipe conducts heat

- oxygen supplied for complete combustion of food

- stirrer to distribute heat evenly

- insulation and lid is present, so less heat loss

- food is enclosed, so less energy lost to surroundings

Describe the process of peristalsis

-Peristalsis is a wave-like motion that moves food along gut

- CM contract and LM relaxes

- Lumen is constricted and food is pushed forward

- In front of the food, CM relax and LM contract, so lumen widens

Name 2 insoluble molecules in food that contain energy

where is bile made?

1) starch

2) Protein

- bile is made in the liver

function of:

Carbohydrates

Proteins

Lipids

Water

Carbohydrates:

- main source of energy

Proteins:

- for growth and repair

- used as enzymes, antibodies and hormones

Lipids:

- insulation and store of energy

Water:

- needed for chemical reactions to occur in cells

where are these digestive enzymes made:

protease

amylase

lipase

protease - pancreas, stomach

amylase - pancreas salivary glands

lipase - pancreas

(duodenum receives these enzymes and secreates them)

Explain the role of bile in digesting lipids

- Emulsifies lipids

- Digests large lipid droplets into small lipid droplets

- Provides more SA for enzyme activity

- Neutralizes HCl acid providing optimum pH for lipase

- Lipase digests lipids into fatty acids and glycerol

Describe the structure of kidney (refer to structure of nephron)

-The kidney contains inner medulla(pyramids) and outer cortex

-The kidney has many nephrons.

-Nephrons have a glomerulus (ball of yarn) surrounded by bowman's capsule.

-Nephrons also have convoluted tubules, loop of Henle and collecting duct

-Renal artery present that carries blood to kidney.

-The ureter carries urine from kidney to bladder

How concentration of blood is restored in a dehydrated person. (blood more concentrated)

- Increased blood concentration is detected by osmoreceptors in hypothalamus

- hypothalamus will stimulate pituitary gland to release ADH

(in reverse scenario, pituitary releases less ADH)

- causes collecting duct to become more permeable

- more water reabsorbed into blood

- less urine excreted

Define excretion.

What substances are excreted from which parts of body?

-removal of metabolic waste

- CO2 from lungs, urea from kidney, sweat from skin

(NOTE: feces are egested, NOT excreted)

Osmoregulation

maintaining salt and water level in body

Define homeostasis. Give 3 examples.

the maintenance of a constant internal environment

examples: body temperature, glucose level, water level

role of skin

- controls heat loss

- prevents water loss

- acts as barrier, to prevent entry of pathogens

- sense organ for touch, pressure and pain

what happens to body when in a COLD place (role of skin)

blood vessels:

- vasoconstriction occurs

- less blood flow to surface of skin

- less heat transfer by radiation

hair:

- hair erector muscle contracts, so hairs pulled upright

- traps air, so less heat transfer by radiation

Sweat gland:

- produces less sweat, so less heat transfer by evaporation

- shivering, where muscles contract releasing energy

what happens to body when in a HOT place (role of skin)

blood vessels:

- vasodilation occurs

- more blood flow to surface of skin

- more heat transfer by radiation

hair:

- hair erector muscle relaxes, so hairs lay flat

- traps less air so more heat transfer by radiation

Sweat gland:

- produces more sweat, so more heat transfer by evaporation

composition of urine

ions, water, urea

Describe how structures in kidney allow correct substances to stay in blood.

-Large molecules such as proteins can't enter bowman's capsule (but small molecules such as glucose can)

- so they are filtered out by ultrafiltration process

-Glucose and amino acids reabsorbed back into blood

- by selective reabsorption process

- in the PCT via active transport

(as glucose is important for respiration and energy)

-Water reabsorbed from collecting duct(via osmosis)

one artificial method to reproduce plants asexually

Cuttings

Role of placenta

- Provides fetus with oxygen and glucose from mother

-Removes waste products such as urea and co2 from fetus, and sends it to mother

-Provides fetus with antibodies

-Produces hormones such as progesterone

[placenta is attached to baby by unbiblical cord, so while good stuff can enter baby via placenta, so can viruses]

what does sterile mean in sex context

how it affects male and female

infertile.

- for males they do not produce sperm

- for females they do not produce egg

therefore no fertilization occurs, and no offspring produced

(this cud be a good thing, like making harmful mosquitos or bacteria sterile prevents their spreading of diseases, as no offspring.)

male reproductive part of plant:

male gamete of plant:

female reproductive part of plant:

female gamete of plant:

male reproductive- stamen which consists of ;

filament holding the anther(produces pollen grain)

male gamete: pollen grain

female reproductive- pistil which consists of;

style holding stigma(where pollen lands) and ovary

female gamete: ovum/egg cell

Describe the events of growth of pollen tube followed by fertilization leads to seed and fruit formation

- Pollen lands on stigma , germinates forming pollen tube

- Pollen tube grows down style into ovule

- Male gamete (pollen) fuses with female gamete (egg)

- Ovule becomes seed

- Ovule wall becomes seed coat

- Ovary becomes fruit

Adaptations/ features of wind pollinated flower

- small, light pollen grains

- stigma is feathery

- small petal

- anther/ stamen is exposed

what are the differences between sexual and asexual reproduction

Asexual:

- only 1 parent needed, so no gametes present

- involves mitosis

- no fertilizations takes place

- produces genetically identical offspring(no genetic variation)

Sexual:

- 2 parents needed, so gametes present

- involves meiosis

- fertilizations takes place

- genetic variation

Adaptations/ features of insect pollinated

- large petal

- enclosed stamen(prevents self pollination)

- big, sticky pollen grain

- stigma is sticky (so that insect can get stuck)

- nectar

function of progesterone in menstrual cycle

-Maintains uterus lining (keeps it thick)

- inhibits release of FSH and LH

(progesterone is secreted from both placenta and ovaries)

One natural method to reproduce plants asexually

Runner

Function of oestrogen in menstrual cycle

-inhibits release FSH

- stimulates release of LH (so that ovulation can occur)

- repairs uterus lining

(during puberty, oestrogen stimulates secondary sexual characteristics like bigger breasts)

explain the graph of menstrual cycle