Additional Science- B3

  • Created by: Janviixo
  • Created on: 03-09-15 17:37



Nucleus- contains DNA (chromosomes)

Cell Membrane- holds cell together, controls what goes in and out

Cytoplasm- gel like substance, most chemical reactions occur

Mitochondria- reactions involving respiration take place: Provides energy to cells e.g. muscle cells and liver cells.

Ribosomes- proteins are synthesised here: too small to see with microscope


Cell Wall- made of cellulose, supports cell

Vacuole- large structure contains cell sap (sugar and salts)

Chloroplast- photosynthesis happens

1 of 21


Chromosomes- made of coiled up DNA, long molecules

DNA divided in short sections: genes

DNA strands made up of small groups called "nucleotides" which contains a small molecule called a "base"

Bases form cross links to keep 2 strands strongly wound together

Complementary Base Pairing: A-T   C-G

Watson and Crick: 1st to model DNA 1953- Used data from other scientists, X-ray data (showing double helix), other data showing bases occurred in pairs

DNA copies itself when cells divides

Unzips, free nucleotides join on using CBP which makes exact copy on other strand.

2 of 21

Protein Synthesis

DNA controls protein synthesis in cell

Genes code a particular protein

Proteins made of chains of amino acids,

different number of AA + different order = different proteins + different shape

different shape = different function

amino acids coded by 3 bases

Proteins made in cytoplasm by ribosomes using code in DNA

mRNA- molecule, copies code from DNA, carries code between two, acts as messanger

3 of 21

Functions of Protein

Carrier Molecules- transport smaller molecules e.g. haemoglobin 

Hormomes- carry messages around the body e.g. insulin

Structural Proteins- physically strong e.g. collagen strengthens connective tissue

Enzymes- control cell reactions

Increase RoR in cell by increasing temp- has optimum temp, denature

Enzymes act as biological catalysts, substance that speeds up reaction without being changed or used up

Substrate- molecule changed in the reaction

Enzyme has active site- part joins to substrate to catalyse reaction

ONLY works with 1 substrate (high specificty)

4 of 21


Temp changes rate an enzyme catalyses a reaction

High temp, increases RoR- More heat = enzyme and susbstrate particles having more energy and higher collision rate

Too hot = bonds in enzyme breaking, changes shape, can't function 

Optimum Temp = 37C

pH has an effect on enzymes- too high/ low interferes with bonds

Optimum pH= 7 or neutral (not always)

Q10 shows how RoR changes when temp is raised by 10C

Q10 = rate at higher temp/ rate at lower temp

5 of 21


Mutations are a change in DNA base sequences

If occurs in a gene, could stop production of proteins or different protein is produced

Wrong or no protein = disaster... may be important enzyme...reproductive systmem = abnormality development

body cells = cells multiply = cancer

SOMETIMES proteins produced after mutations can be beneficial- improvement on one supposed to be. Gives organism a survival advantage over rest of population, passed on to offspring, mutation becomes common (natural selection and evolution)

Ionising radiation causes mutations- incl. x-rays and UV light 

Chemicals (mutagens) cause mutations, if causes cancer known as carcinogens e.g. cigarette smoke

6 of 21

Multiplying Cells

Single celled organism = bacteria... aren't in danger of extinction 

Multicellular- can be bigger, travel further, get nutrients variety of ways, allows cell differentiation (different cells for different jobs), specially adapted for particular job, can be more complex

however...needs to have specialised organ systems incl. system to communicate, supply nutrients, controls the exchange of substances

"Mitosis is when a cell reproduces itslef by splitting to form two identical offspring"

1) DNA is replicated

2) DNA coils into double-armed chromosomes

3) Chromosomes line up at centre, then divide as cell fibres pull them apart. The 2 arms go to opp poles.

4) Cytoplasm divides, get 2 new identical cells

7 of 21


Meiosis creates gametes in ovaries and testes

Body cells of mammals are diploid- 2 copies of chromosomes in nucleus

Gametes are haploid- 1 copy of each chromosome

1) DNA replicates

2) Chromosomes arrange into pairs. 

3) In 1st division the pairs split- chromosome in each pair move to opp poles. In each of the 2 new cells, no pairs 

4) The 2nd division of meiosis is like mitosis- each chromosome splits in half, 1 arm ends up in each cell

5) 4 unidentical cells

8 of 21


Creates genetic variation

Male and female gametes combine to form diploid cell- cell called zygote

Characteristics of zygote controlled by combination of genes on its chromosomes

Inherited genes from both parents, so shows features of either one but not exactly like them

Sperms function is to transport males DNA to females egg

Sperm- small, long tails to swim, lots of mitochondria (provide energy to swim), acrosome front of head (release the enzymes they need to digest their way through membrane off egg)

9 of 21

Stem Cells & Differentiation

Animals grow to finite size, grow by cell division. Plant grow continuously, grow in height by cell enlargement (elongation), growth by cell division happens in meristems (tips, roots, shoots)

Differentiation = cell changes to become specialised for particular job e.g. white blood cells

Some cells are undifferentiated, develop into types of cells, tissues and organs.

^ STEM CELLS, found in human embryos, potential to turn into any kind of cell

Adults have stem cells e.g. bone marrow BUT can't turn into any cells, only certain ones

stem cells cure diseases. Blood disorders cured by bone marrow transplant. Early human embryos have lots of stem cells, scientists extract these and grow them. (stem cell therapy)

People against stem cell research, embryos shouldn't be used (potential life), human life important than embryos, usually unwanted embryos used

Stocks of stem cells scientists use. Some countries (e.g. USA) won't fund research to make new stem cell stocks

10 of 21


Growth- increase in size or mass

Measure growth by length, wet mass and dry mass

Length- easy to measure BUT doesn't tell you changes in width, diameter, no. branches etc

Wet mass- weigh organism, easy to measure BUT WM is changeable (recently rain/ full bladder)

Dry mass- dry out organism, not affected by water or food eaten BUT kill to weigh, not good to work out dry mass of a person! (best measure of growth)

Human growth has 5 phases - infancy (1st 2yrs, rapid), childhood (-puberty, steady), adolescence (-growth complete, rapid), maturity/adulthood (growth stops), old age

Organisms grow unevely, some faster than others. Baby developing in womb, brain grows at greater rate

11 of 21

Aerobic Respiration

Respiration- releasing energy from glucose. Happens in every cell, can't be used directly by cells: used to make substance ATP

ATP acts as energy source for many cell processes and transports energy where needed

Respiration controlled by enzymes. RoR affected by temp and pH (see card 5)

Aerobic Respiration needs oxygen- most efficent way to energy 

glucose + oxygen -----> carbon dioxide + water + (energy)

C6H1206 + 602 ------> 6C02 + 6H20

When RoR increases, oxygen consumption & carbon dioxide production increase

Rate of oxygen consumption can be used to estimate metabolic rate (energy being used)

12 of 21

Anaerobic Respiration

When you do vigorous exercise, body can't supply enough oxygen to muscles.

Anaerobic respiration = without oxygen

Not the best way to convert glucose to energy- releases much less energy per glucose molecule

Glucose is partially broken down and lactic acid is also produced

Lactic acid builds up, leads to pain and fatigue in muscles

Glucose ----> Lactic Acid + (Energy)

Adv- keep using muscles

After resorting anaerobic resp. when you stop, you'll have oxygen debt... need oxygen to break down lactic acid, you keeping breathing hard after you stop exercising. Lactic acid carried to liver - heart rate stays high

RQ= amount of CO2 produce/ amount of O2 used..... 0.7-1 = aerobic......>1 = anaerobic

13 of 21

Functions of Blood

Plasma- liquid bit of blood, pale yellow, carries:

1) Water 2) Digested food e.g. glucose, amino acids 3) Carbon dioxide 4) Urea 5) Hormones e.g. insulin  6) Anitbodies 7) Red, white blood cells and platelets 

RBC- oxygen from lungs to cells in body, small, biconcave shape gives large SA:V for absorbing and releasing oxygen.

Haemoglobin gives blood its colour- contains iron, in lungs becomes oxyhaemoglobin 

In body tissues- oxygen is released

RBC- no nucleus, frees up space for haemoglobin, easily flow through tiny capillaries 

14 of 21

Blood Vessels


carry blood under pressure, walls are strong, thick and elastic, thick layer of muscle. Lumen is small

CAPILLARIES- involved in exchange of materials

Really small, arteries branch into capillaries, carry blood close to every cell to exchange substances, permeable walls to allow diffusion of substances, supply food and oxygen, carries waste (CO2)

Walls are 1 cell thick- increases rate of diffusion by decreasing the distance over occurance

VEINS- back

blood at low pressure, walls not as thick, bigger lumen help blood flow, has valves to keep blood flowing in right direction

15 of 21

The Heart

Mammals have double circulatory system, 1st connects heart to lungs- deoxygenated blood pumped to lungs, 2nd connects heart to rest of body- oxygenated blood pumped out to body, releases, deoxygenated blood returns to heart and goes to lungs.

Adv- blood returning means blood can be pumped at higher pressure, increases rate of blood flow, more oxygen delivered to cells. Mammals use up oxygen to maintain body temp.

1) Right Atrium recieves deoxygenated blood from body (vena cave)

2) D.O blood moves through right ventricle, pumps to lungs (pulmonary artery)

3) Left Atrium recievs oxygenated blood from lungs (pulmonary vein)

4) Oxygenated blood moves through left ventricle, pumps to body (aorta)

5) Left ventricle has thicker wall, needs more muscle to pump around body

6) Semilunar, trucispid and bicuspid valves prevent backflow

16 of 21

Selective Breeding

SB- humans artificially select plants/ animals to breed and have genes remain in population according to what we want

Organisms are selectively breeds to develop best features e.g. max. yield, good health, qualities (speed, attractiveness, temperament)

Select best characteristics from stock, breed them, select best offspring and breed them together, continue process over generations 

Disadv- reduction in gene pool in population, breeding cloesly related organisms = inbreeding

inbreeding causes health problems (genetic disorders), breeding closely related organisms mean recessive alleles more likelt to build up

Serious problem if new disorder appears as not much genetic variation in population. All stocks closely related so if 1 were to die to it then others would be likely to succumb to it

17 of 21

Genetic Engineering

Idea of genetic engineering to move genes from 1 organism to another to produce useful biological products

Adv- produce new and useful organisms quickly

Disadv- gene may have unexpected harmful effects

Gene of desirbale characteristics selected, cut from DNA and isolated, inserted into DNA, organism replicates 

Scientists take gene that controls beta-carotene production from carrots and put in rice plants, humans change gene to vitamin A

Gene for human insulin production put into bacteria, extracted from medium as produced

Plants with resistance, gene is cut out and put on useful plants

People believe it's wrong to gentically engineer organisms for human benefits. Evolutionary consequences are unknown

18 of 21

Gene Therapy and Cloning Animals

Involves altering genes to cure genetic disorders

2 types- 1st changing genes in body cells 2nd changing genes in gamete cells, every cells of offspring would be affected (illegal for humans)

May have unexpectde consequences, cause new problems. Could lead to 'Designer babies'

CLONES- genetically identical organisms ('Dolly' the sheep)

Dolly produced by nucleus transfer- placing nucleus of body cell to egg cell

Nucleus of egg cell removed (no genetic info) replaced with other nucleus (diploid nucleus from udder cell of different sheep. Cell was given electric shock to start dividing by mitosis, dividing cell (embryo) implanted into uterus 

19 of 21

Uses and Risks of Cloning Animals

Benefits- cloning allows to mass produce desirbale characteristics. Animals have organs that are transplantable into humans (e.g. pigs). Human embryos can be produced by cloning adult cells, used to supply stem cells

Risks- cloned animals might not be as helathy as normal ones. Cloning is a new science and might have consequences that wer'e not aware of yet.

Cloning humans has ethical issues:

1) lots of surrogate pregnancies, high rate of miscarriage and stillbirth

2) Clones of mammals seen to be unhealthy and die prematurely 

3) Even if healthy clone was produces, might be psychologically damaged by knowledge of being a clone of someone else.

20 of 21

Cloning Plants

Gardeners take cuttings from plant and plant them to produce clone of mother plant

Easier to clone plants as they keep ability to differentiate unlike animals who lose ability at early stage

Commercial cloning involves tissue culture

Choose plant, remove several pieces of tissue from parent at tips, grow tissue in growth medium containing nutrients and growth hormones (done under aseptic conditions), as tissue produces shoots/roots it can be moved to potting compost

Adv- fairly sure of characteristics as genetically identical to parent, don't waste time or money, possible to mass produce plants that are hard to grow from seeds

Disadv- may suffer from disease due to change in environment, unusual problems with lack of genetic variation

21 of 21




All the key information in note form - very effective, good work

Similar Biology resources:

See all Biology resources »See all B3 resources »