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Why are cells the smallest unit of life?

They are surrounded by a membrane and although there are smaller things that live in cells they are not the smallest unit of life because they require cells around them to live


Why do we need cells for energy?

They are the site of all chemical reactions for life


What are exceptions to cell theory?

- striated muscle cell
- aseptate fungal hyphae
- giant alga


Why is striated muscle cell an exception to cell theory?

The size is irregular ( can be up to 30cm long) and each cell has multiple nuclei ( between 2 and 180)


Why is aseptate fungal hyphae an exception to cell theory?

Instead of having cell- like sections, a hypha is an uninterrupted tube like structure with many nuclei spread along it


Why is giant alga an exception to cell theory?

A uni cellular organism which is 10 cm in size


What are the 7 fundamental processes for life in unicellular organisms?



What is metabolism?

The speed at which reactions take place in an organism


What is homeostasis?

Maintaining a constant internal environment suitable for all processes for survival


What is excretion?

The removal of waste, to avoid poisoning


What is nutrition?

Everything needs to take in some form of food in order to release energy necessary for other body processes


How does paramecium carry out the 7 functions of life?

Metabolism- cytoplasm
Reproduction- divides by mitosis
Homeostatis- has a contractile vacuole, which manages the water content
Growth- consumes and assimilates biomass then gets larger until it divides
Response- cilia
Excretion- plasma membrane controls what leaves the cell
Nutrition- food vacuoles store organisms that paramecium has consumes


How does an increasing surface area in a cell affect the volume: surface area ratio?

As the total surface area increases, the ratio between the surface area: volume decreases


Why is it important for a cell to have a high SA:V ratio?

If the ratio is too small, substances will not diffuse into the cell as quickly as they are required to.
If the rate is too small the waste products are unable to leave the cell and will accumulate, produced more rapidly than they can be excreted


What happens as a result of cells being too big?

They will reproduce and divide by mitosis , as if it gets too hot, waste products cannot be excreted fast enough and diffusion isn't occurring fast enough


How do unicellular and multicellular organisms maximise SA:V ratio?

Unicellular- cilia( root hair cells, villi)
Multicellular - folding up ( e.g. Alveoli in lungs)


What is leukaemia?

Cancer of blood and bone marrow, abnormal white blood cells that do not function properly. Thought to originate in blood stem cells.


How is leukaemia treated?

Bone marrow transplants containing stem cells ( haemotopoietic stem cell transplant ), differentiate to form healthy white blood cells.

Chemotherapy and radiotherapy destroy white blood cells


What are side effects of leukaemia treatment?

- infections from donor
- graft- versus- host disease ( rejection- cells implanted attack cells from host body)


What is stargardt disease?

Progressive vision loss that can effect children. It is a recessive genetic condition.


What is treatment for statgardt disease?

Growing retinal pigment epithelium cells from stem cells and injects under retina, supports photo receptor with results


What are the steps in therapeutic cloning?

1. Nucleus of an ovum removed and replaced with somatic cell of patient
2. Cell administered electric shock- starts dividing
3. Blastocyst stage- genetically identical tissues for patients


What are the terms of stem cell research?

It is allowed to research stem cells from embryos but they must be destroyed after 14 days to avoid human cloning


What are factors of using embryos for stem cell research?

- obtained from IVF excess embryos
-destructs embryos- ethical issue
- growth potential almost unlimited
- High risk of tumours
- can differentiate any cell type
- less chance of genetic damage
- not genetically identical to patient


What are factors of using umbilical cord blood for stem cell research?

- easy extraction but limited quantities
- ethically ok- umbilical cord is discarded anyway
- reduced growth potential
- lower risk of tumours
- limited capacity for differentiation- blood cells
- less chance of genetic damage
- not genetically identical to patient


What are factors of using adults for stem cell research?

- stem cells difficult to obtain
- adults can give permission
- reduced growth potential
- lower risk of tumours
- limited capacity for differentiation- depends on source tissue
- genetic damage can occur as mutations accumulate throughout life
- fully compatible as genetically identical to patient


What are the benefits of an electron microscope?

Have a much higher resolution than light microscopes

Reveal the ultra structure of cells


What is the formula for the magnification of an electron microscope?

A x M


What is resolution?

The shortest distance between 2 points that can be distinguished


Properties of prokaryotes?

- unicellular organisms like bacteria
- no nucleus, DNA located in nuclear area
- smaller than eukaryotic cells
- cell wall
- contain plasmids
- DNA in single loops
- no mitochondria
- 70 ribosomes
- free floating DNA in cytoplasm


What are the stages of binary fission in prokaryotic cells?

- DNA replicated and attaches itself to the plasma membrane
- the cell elongates to separate chromosomes
- membrane invaginates, pulling itself together in the middle
- the cell splits into 2 daughter cells


Properties of eukaryotes

- larger sized cell
- no cell wall, except in plants
- DNA associated with histoine proteins
- no plasmids
- DNA in separate chromosomes
- DNA in membraned nucleus
- has mitochondria
- 80 ribosomes


Similarities between prokaryotes and eukaryotes?

Cell membrane, DNA, ribosomes, metabolism, require energy, cytoplasm


What is an animal extra-cellular matrix?

A secretion, sometimes if glycoproteins. It sits between cells and can perform many additional functions such a support, adhesion, filtering, as well as a basis for the formation of tissue


What happens when phospholipids are out in water?

An emergent property is that phospholipids will self organise to keep their hydrophilic heads wet and hydrophobic tails dry


What is micelle?

A formation where hydrophilic heads face the water and tails join to avoid water


What is a liposome?

Liposomes have a bilateral formation to contain water inside the cell but still keep it away from the membrane


What is a phospholipid bilayer?

This is arranged with the hydrophilic phosphate heads facing outwards and the hydrophobic fatty acid tails ( consisting of hydrocarbon chains) facing into the middle of the bilayers. It is a barrier against all molecules except the smallest, CO2 and O2.


What are integral proteins?

They are usually involved in transporting substances across the membrane and usually span from 1 side of the phospholipid bilayer to the other


What are peripheral proteins?

They sit on surfaces and slide around the membrane quickly and collide with each other, but will never flip from one side to another. The ones on the inside of the membrane are involved in maintaining cells shape or motility. Might also be enzymes.


What are glycoproteins?

Usually involved in cell recognition, which is part of the immune system. Also act as reception a in cell signalling such as with hormones


What is cholesterol?

It binds together lipid in the plasma membrane, reducing its fluidity as conferring its structural stability


What is a fluid mosaic model?

The structure of a membrane in fluid state, on electron micrographs the proteins form a mosaic pattern


How is the structure of phospholipids strong?

- hydrophobic hydrogen tails attracted to each other
- hydrophilic phosphate heads attracted to each other
- heads suited to high water content of tissue fluid and cytoplasm on either side of membrane
-Tails repel water, creating a barrier between the internal and external water environments of the cell + a barrier to movement of charged molecules
- charges in phospholipids attract them, making them stable but allowing some movement
- presence of cholesterol molecules increases stability


What do channel proteins do?

Span membranes, movement of large molecules. There are passive and active membrane pumps- allow specific ions through


What do receptor proteins do?

Detect hormones arriving at cell to signal changes in function involved in other cell and substance recognition.


What are electron carriers?

Chain of peripheral and integral proteins that allow electrons to pass across the membrane. Active pump uses ATP to move specific substances across the membrane


How do substances pass through selectively permeable membranes?

- some molecules pass through easily or go through a tunnel ( facilitated diffusion)
-other molecules need energy in active transport
- large molecules use own membrane ( endocytosis/ exocytosis)


Does endocytosis require energy?

Yes- ATP to form vesicles


Cellular example of endocytosis?

Placenta- proteins from mothers blood absorbed by foetus in endocytosis


Does exocytosis require energy?



Cellular example of exocytosis?

Digestive enzymes released from glands


Removal of excess water


Does simple diffusion have a concentration gradient?



Cellular example of simple diffusion

Lungs- alveoli


Does facilitated diffusion use membrane proteins?

Yes- channels


Does facilitated diffusion have a concentration gradient?

High to low


Cellular example of facilitated diffusion

Water in/ out of cells

Glucose and amino acids in/ out of body cells


What is the process of endocytosis?

A vesicle is formed- a small region of membrane pulled from the rest and pinched off ( using proteins and ATP). The vesicle consists of a small piece of plasma membrane and contains material from outside of the cell


What is a vesicle?

A small sac of membrane with fluid inside. Present in eukaryotes. Constructed, moved and deconstructed.


Why is endocytosis needed?

To carry water and solutes and larger molecules that cannot pass across the plasma membranes


What is the purpose of exocytosis?

Vesicles are used to release materials from cells by fusing with the plasma membrane. - secretion, excretion


How does endocytosis and exocytosis work within the process in a secretory cell?

1. Endocytosis- plasma membrane pulled inwards - fluid enclosed when vesicles picked off
- vesicles move through cytoplasm carrying contents

2. Proteins synthesised by ribosomes and let them enter rough endoplasmic reticular ( RER)

3. .Vesicles bud off from RER and carry proteins to Golgi apparatus

4. Golgi apparatus modifies the proteins

5. Vesicles bud off from Golgi apparatus and carries modified proteins to plasma membranes

6. Exocytosis - vesicles fuse with plasma membrane
- contents of vesicle expelled
- membrane flattens again


What is simple diffusion?

- net movement from high- low concentration
- can only happen if phospholipid bilayer is permeable to the particles
- non polar particles ( oxygen) diffuse easily
- centre of membrane is hydrophobic do ions don't easily pass through
- polar molecules ( partial charges) can diffuse at low rates


What is facilitated diffusion?

- ions and particles that cannot diffuse between phospholipids exit/ enter if there are channel through plasma membrane
- channels consists of proteins- narrow diameter
- diameter and chemical properties endure only one specific particle enters
- high - low concentration


What is osmosis?

- net movement of water particles, due to concentration of substances dissolved in water ( more intermolecular bonds)
- bonds restrict movement of H2O - high dilute concentration- low concentration
- passive
- all cells
- some cells have aquaponics - increase permeability to water


What is active transport?

- substances absorbed/ expelled against concentration gradient
- used ATP
- carried out by globular proteins in membranes


What is an axon?

Part of a neutron
- tubular membrane and cytoplasm
- narrow as micrometer in diameter
, metre in length
-carries nerve impulses


What does nerve impulses involve chemically?

It involved rapid movement of sodium and potassium ions across the axon membrane


How does sodium and potassium move across the axon membrane in nerve impulses?

Facilitated diffusion though sodium and potassium channels


What happens in the cycle of the sodium- potassium pump?

1. Interior pump open to inside of axon-3 sodium ions enter and attach to binding site
2. ATP transfers phosphate group to the inside of the pump- changes sharp and closes
3. Interior of pump opens to outside of axon and 3 sodium ions are released
4. 2 potassium ions from outside enter and attach to binding site
5. Binding of potassium causes release of phosphate group causing pump to change shape
6. Interior of pump opens to inside of axon and 2 potassium ions are released


What are the properties of potassium channels?

- 4 protein subunits
-narrow between subunits- allows K ions in either direction
- pore 0.3nm wide at narrowest
- they are voltage gated due to an imbalance of charges across the membrane
- if an axon has more positive charges outside than inside the potassium channels are closed


How do potassium channels work?

- K ions dissolve- bonded to shell of H2O molecules that make them too large to pass through the pore
- the bonds between the K ion and surrounding H2Os are broken and bonds form temporarily between K ion and series of amino acids in narrowest part of the pore
- after they have passed through the channel, the K ions again become associated with a shell of H2O molecules


What is spontaneous generation?

Formation of living organisms from non living matter


Who made claims of spontaneous generation and why?

Theophratus, Aristotle and Paracelsus due to no understanding of cells, microorganisms and sexual reproduction


What was Louis Pasteur's experiment that proved spontaneous generation wrong?

- he had a nutrient broth of water yeast and sugar
- if sealed it remained unchanged
- when a pad of air filtered cotton wool was placed in the broth, in 36hrs there was mould

- broth in swan neck glasses
- longer glasses- no mould
- boiled- no mould


Why is there no spontaneous generation of cells?

Cells are highly complex structures and there are no natural mechanisms for producing cells from simpler sub units

Cell division has to happen.

Viruses are produced from simpler sub units but they don't consist of cells and are produced from hosts


How did miller and Urey form carbon compounds?

They passed steam through a mixture of methane, hydrogen and ammonia ( early earth atmosphere)

Electrical discharges to stimulate lightening

Amino acids and other carbon compounds for life were produced, showing that organic molecules were synthesised outside cells with no oxygen


How do carbon compounds naturally form polymers?

Origins of the first carbon compound are in deep sea vents ( cracks in the surface, gushing hot water with reduced inorganic compound like iron sulphides).

This represents a source of energy for these carbon compounds = polymers


How were membranes naturally formed?

- phospholipids and amphipathetic carbon compounds 1st would have naturally assembled into bilayers

- bilayers form vesicles resembling plasma membrane


How did there come a mechanism for inheritance?

- genes made of DNA, enzymes as catalysts for replication
- for enzymes to be made, genes are needed
- solution= RNA used to be genetic material- self replicating and a catalyst


How did mitochondria form eukaryotic cells?

1. Mitochondria- once free living prokaryotic organisms developed aerobic respiration.
2. Larger prokaryotes with anaerobic respiration took them in by endocytosis- small prokaryotes lived in their cytoplasm
3. They grew and divided as fast as the large ones- became mitochondria inside eukaryotes today


What can we describe the relationship between mitochondria ( prokaryotic organisms with aerobic respiration) and large prokaryotes with anaerobic respiration as?

Symbiotic relationship, mutualistic relationship

- as the small one is supplied food by the larger one
- as the small aerobically respires providing energy for the large cell


What does endosymbiosis also explain the origin of?

Chloroplasts with small photosynthesising cells being able to divide in a large cell


What evidence is there for endosymbiosis?

- mitochondria and chloroplasts have their own gene on a circular DNA molecule, like prokaryotes

- have own 70s ribosomes of shape and size of prokaryotes

- transcribe own DNA and use mRNA to synthesise own proteins

- only produced by division of pre existing mitochondria and chloroplasts


What is mitosis?

When the nucleus of a eukaryotic cell divides to form 2 genetically identical nuclei


What phases does mitosis consist of?

Prophase, metaphase, anaphase, telophase


What has to happen before mitosis?



What happens in interphase?

- DNA replication

-many metabolic reactions occur- DNA replication, protein synthesis only happen in interphase

- number of mitochondria in cytoplasm increase- growth and division

- in plant cells and algae chloroplasts increase in the same way

- also synthesise cellulose and use vesicles to add it to their walls


What is the cell cycle?

Sequence of events between 1 cell division and the next- interphase and cell division


What is the sequence of the cell cycle?



G1- cellular content apart from chromosomes are duplicated

S- each of the chromosomes are duplicated



What are the stages in prophase?

1. Chromosomes condense

2. Centrioles formation

3. Nuclear membrane breaks down


What are the stages of metaphase?

1. Spindle fibres form at centrioles
2. Chromosomes line up at the equator


What are the stages of anaphase?

1. Spindle fibres shorten and pull chromatids apart to opposite poles


What are the stages of telophase?

1. Nuclear envelope reforms
2 spindle disappears
3. Chromosomes uncool
4. Cytokinesis


What is cytokinesis?

When cells divide after mitosis if two genetically identical nuclei are present in a cell


How does cytokinesis happen in animal cells?

- the plasma membrane is pulled inwards around the equator of the cell to form a cleavage furrow

- punches cytoplasm in half


How does cytokinesis occur in plant cells?

- Golgi apparatus forms vesicles of new cell wall materials
-vesicles collect at equator and coalesce to form membrane


What are cyclins?

Proteins that control the cell cycle


How do cyclins work?

- cyclins bind to enzymes called cyclin dependent kinases

- become active and attach phosphate groups to other proteins in the cell

- this triggers activity to carry out tasks specific to a phase in the cell cycle


What does each type of cyclin do in the cell cycle?

Cyclin D- triggers cell from G0 to G1 and G1 to S phase

Cyclin E- prepares cell for DNA replication in S phase

Cyclin A- activates DNA in nucleus in S phase

Cyclin B- promotes assembly of mitotic spindle and other tasks in the cytoplasm to prepare for mitosis


Who discovered cyclins?

Tim hunt


How were cyclins discovered?

-During research into the control of protein synthesis in sea urchin eggs

- discovered protein that increased in concentration after fertilisation and then decreased in concentration, whereas other proteins to increase

-protein being synthesised over a period of 30 minutes and after was being broken down

-went through repeated increases and decreases in concentration that coincided with phases of cell cycle


What are benign tumours?

Abnormal groups of cells that adhere to each other and do not invade


What are malign tumours?

Cells that can come detached and form secondary tumours


What are carcinogens?

Chemicals and agents causing cancer


What are mutations?

Random changes to the base sequences of genes


What are oncogenes?

Genes that become cancer causing after mutating


What is metastatis?

The movement of cells from a primary tumour to set up secondary tumours in other parts of the body


What is the function of the nucleus?

Cell management


What are the purpose of centrioles?

During cell division they replicate and grow spindle fibres


What is the purpose of mitochondria?

Site of aerobic respiration


What is the purpose of chloroplasts?



What is the purpose of ribosomes?

Protein synthesis


What is the purpose of rough endoplasmic reticulum?

Ribosomes are attached to them, so protein synthesis and discharge of products from cells


What is the function of the soft endoplasmic reticulum?

Synthesis of substances for cells ( lipids )


What is the function of the Golgi apparatus?

Synthesis of bio chemicals