Biologi

Binary fission occurs in what type of cell?

Prokaryotic cell

Where is genetic information contained in this type of cell?

Plasmids, circular DNA

Explain the process of binary fission?

Bacteria replicate by binary fission

Replication of the circular DNA

Division of cytoplasm to produce 2 daughter cells

Each with single copy of circular DNA

Why are viruses difficult to treat and develop medicines against?

Viruses replicate inside human host cells, making it hard to target without damaging healthy cells.

What is the definition of mitosis?

Production of 2 genetically identical daughter cells that have the same amount of chromosomes as the parent cell and each other.

where does mitosis occur?

body cells

What is the definition of a homologous chromosome?

Two chromosomes that carry the same genes.

What are the 5 stages of mitosis?

Interphase
Prophase
Metaphase
Anaphase
Telophase

Describe the entire process of mitosis?

Interphase -
Chromosomes are dispersed (not visible)
Each chromosomes replicate
Chromosomes made up of 2 sister chromatids joined together by a centromere

Prophase -
Chromosomes shorten and thicken to become visible
Chromosomes appear as two sister chromatids joined at the centromere
Centrioles move to the pols of the cell and start forming spindle fibres

Metaphase -
Chromosomes line up on the equator
Chromosomes attached to spindle fibres by their centromere

Anaphase -
Spindle fibres contract
Centromere splits
Sister chromatids are pulled to opposite poles

Telophase -
Chromosomes uncoil and become thinner
Nuclear envelope reforms
cytokinesis begins

Definition of meiosis?

Production of 4 genetically different daughter cells that have half the number of chromosomes as the parent cell (haploid)

define the term “haploid”?

half the number of chromosomes.

Define the term “Diploid”?

2 complete sets of chromosomes, one set from each parent.

Where does meiosis occur?

Sex cells (gametes)

Explain the entire process of meiosis?

Interphase -
Chromosomes are dispersed (so not visible)
Each chromosome replicates

Prophase 1 -
Chromosomes shorten and thicken to become visible.
Chromosomes appear as two sister chromatids joined at the centromere.
Homologous pairs of chromosomes form bivalents
Chiasma form where the chromosomes cross over each other
This produces a new combination of alleles

Metaphase 1 -
Homologous chromosome (in bivalents) line up on the equator
chromosomes attached to spindle fibres by their centromere
Independent segregation of the homologous chromosomes will result in a different combination of alleles within the daughter cells.

Anaphase 1 -
Homologous chromosomes are pulled apart to opposite poles

Telophase 1 -
Chromosomes uncoil and become thinner
cytokinesis begins (splitting of cytoplasm)

Prophase 2 -
Chromosomes shorten and thicken to become visible
Chromosomes appear as a pair of sister chromatids joined at the centromere

Metaphase 2 -
Chromosomes line up on the equator
Chromosomes attached to spindle fibres by their centromere

Anaphase 2 -
Chromatids are pulled to opposite poles

Telophase 2 -
Chromosomes uncoil and become thinner

Cytokinesis -
Cytoplasm divides
Membranes form around new cells

4 haploid cells are produced

Describe the contrast between meiosis and mitosis?

Meiosis -
Reduces the chromosomes number
Only happens in sex cells (gametes)
Produces haploid
Produces 4 daughter cells (genetically different)

Mitosis -
Maintains same chromosomes number as in the parent nucleus
Only happens in body cells
Produces diploid
Produces 2 daughter cells (genetically identical)

How does meiosis result in variation?

Crossing over
Independent assortment

What is crossing over?

Homologous pairs of chromosomes form bivalents. Non sister chromatids wrap around each other. Chromatids break and re-join at points called chiasmata, exchanging equivalent sections of DNA, produces new combination of alleles.

What is independent assortment?

How different combinations of homologous chromosomes can be separated during anaphase 1 leading it to genetically unique gametes.

How does meiosis result in variation?

Homologous chromosomes pair up
Independent segregation occurs
Maternal and paternal chromosomes are re-shuffled in any combination
Crossing over leads to exchange of parts of non sister chromatids/alleles between homologous chromosomes
both create new combinations of alleles

Why meiosis is important in sexual reproduction

Produces haploid cells so fertilisation maintains the chromosomes number in the next generation

What is the cell cycle?

The cell cycle is an ordered set of events leading to cell growth and division

Explain the process of the cell cycle?

Interphase occupies most of the cell cycle
1. G1 phase: synthesis of proteins
2. S phase: DNA is replicated
3. G2 phase: organelles grow and divide, ATP stores increased

Nuclear division:
Mitosis

Cell division:
Cytokinesis

Do viruses undergo cell division?

no, because they are non living

What is cancer?

Cancer is the result of DNA replication errors due to gene damage that disrupts cell mitosis and the cell cycle, causing uncontrolled cell division.

How is cancer often treated?

Blocking some part of the cell cycle, prevent DNA replication, inhibiting the metaphase by interfering with spindle formation

What is the role/function of phospholipid (Membrane)

Forms bilayer
Selectively permeable; only allowing non-polar molecules through the cell
Compartmentalisation; maintain different concentrations either side of the membrane
Flexible shape

within cells:
Selectively permeable; only allowing non-polar molecules through into organelle
separates metabolic reaction and enzymes inside organelle
surface for reactions

What does cholesterol do? (membranes)

regulates fluidity
hydrophobic

What does proteins do (membranes)?

Stability to the membrane
Can be extrinsic (surface) or intrinsic (through the bilayer)
Channel proteins for polar molecules in facilitated diffusion
Carrier proteins for active transport of polar molecules.

What does glycoproteins/glycolipid do (membranes)?

Receptor site for hormones
act as a recognition sites for molecules and cells
helps cells to attach to each other to form tissue

What are the 5 different transport methods

name them all and state if they are passive or active.

Passive:
Diffusion
Osmosis
Facilitated diffusion

Active:
Active transport
Co-Transport

What are the 4 factors affecting rate of transport - explain them

Concentration steepness - the greater the difference in concentration between the 2 sides of the membrane the faster the rate of transport.
explanation: more particles to move from a high to low concentration

Surface Area - The greater the surface area (e.g microvilli present) the faster the rate of transport
explanation: This is because more molecules or ions can cross the membrane at once

Number of proteins - A larger number of channel and carrier proteins in the membrane the faster the rate of transport
This is because more molecules or ions can cross the membrane at once

Higher temperatures - higher temperatures give molecules or ions more kinetic energy so the faster the rate of transport
explanation: Molecules move around faster

Define diffusion

The net movement of lipid soluble molecules from a higher concentration to a lower concentration down a concentration gradient until equilibrium. This is a passive process

Define facilitated diffusion

Net movement of molecules or ions from a higher concentration to lower concentration down a concentration gradient until equilibrium. This is a passive process and uses channel and carrier proteins

Define carrier and channel proteins.

Carrier protein - Water filled hydrophilic pores or tunnels than span the membrane, allowing water-soluble molecules, charged ions to pass through

Channel protein - Proteins that bind to specific solutes such as glucose, and changes their shape to move them across the membrane

Define Osmosis:

The diffusion of water molecules from a higher water potential to a lower water potential down a water potential gradient until equilibrium, this is passive across membrane or aquaporins

Describe the 2 sides of an osmosis movement?

A: Higher water potential
Lower concentration of solute molecules

B: Lower water potential
Higher concentration of solute molecules

What is a solute?

Ion/Molecule that dissolves in a solvent, e.g sodium ions (solute) dissolve in water (solvent)

What is a solvent?

A substance that a solute dissolves in.

What is incipient plasmolysis?

The protoplast no longer pressures on the cell wall.

What is a protoplast?

Consists of outer cell-surface membrane, nucleus, cytoplasm and inner vacuole membranes

Define “plasmolysed”

The protoplast and cell contents pull away from the cell wall

Define the term “turgid”

The protoplast is pushed against the cell wall

In animal cells, describe what happens to net movement of water, state of cell?

net movement of water:
higher (less negative) - the water enters
equal - no net movement of water by osmosis
lower (more negative) - water leaves

state of cell:
higher (less negative) - swell bursts
equal - no change
lower (more negative) - shrinks

In plant cells, describe what happens to net movement of water, state of cell?

net movement of water:
Higher (less negative) - enters cell
equal - neither enters or leaves
lower (more negative) - leaves cell

Protoplast:
Higher (less negative) - swells
equal - no change
lower (more negative) - shrinks

Condition of the cell:
Higher (less negative) - turgid
equal - incipient plasmolysis
lower (more negative) - plasmolysed

How does high sodium concentrations affect blood volume

Sodium ions lower the water potential of blood
Water would move into the blood by osmosis from cells/tissue fluid
increasing the blood volume

Define “active transport”

The movement of ions or molecules from a lower concentration to a higher concentration against a concentration gradient
USING ATP
and carrier proteins

What are the limiting factors for diffusion, facilitated diffusion, osmosis, active transport

diffusion: concentration gradient
facilitated diffusion: proteins, concentration gradient
osmosis: water potential difference
active transport: ATP, Proteins

Explain the process of co transport with glucose

Sodium leave the epithelial cell into the blood
By active transport using the sodium/potassium pump
So sodium concentration inside epithelial cell is lower than the lumen of the ileum
Sodium moves from the lumen of the ileum into the epithelial cell by facilitated diffusion down a concentration gradient
Glucose is absorbed with sodium against glucose concentration gradient
Glucose moves into blood from epithelial cell by facilitated diffusion

What is the function of lysosomes?

Contains hydrolytic enzymes to digest waste material

Why is the cell surface membrane described as a “fluid mosaic”

Phospholipids are able to move, mosaic because of different arrangement of phospholipids and proteins

Define a pathgoen

A micro-organism that causes disease

What is an antigen?

A non self protein that stimulates an immune response causing production of antibodies.

what are some examples where antigens can be found

Abnormal body cells
toxins
pathogens
cells from other organisms of the same species

What is an antibody?

A globular glycoprotein produced by plasma cells in response to specific antigens

What is the immune system?

A system of biological structures and processes that identifies and kills pathogens and tumour cells

What are the stages of defence in the immune system?

Prevent invasion
non specific - phagocytes
specific - lymphocytes
T cell - cell mediated immunity
B cell - Humoral response

Explain the process of phagocytosis?

Phagocyte attracted to pathogen by chemicals and recognise antigens on pathogen as non-self
Phagocyte engulfs the pathogen
The pathogen trapped in a membrane bound pocket called a phagosome
lysosomes fuse with the phagosome and release hydrolytic enzymes into phagosome
The enzymes hydrolyse the pathogen destroying it
antigens form the pathogen are displayed on the surface membrane

Where are the T-lymphocytes and B-lymphocytes made and matured in?

T-lymphocytes
made in = bone marrow
matured in = thymus gland

B-lymphocytes
made in = bone marrow
matured in = bone marrow

Why is specific immunity slower and specific and specific to only one antigen?

Specific: Each pathogen has a specific shaped antigen on its surface, these are different for different types or species of pathogen

it’s receptor is specific to and responds to only one antigen only because: Specific lymphocytes exist in the body already, there are millions of different types which each recognise a different antigen, They have receptors on the surface that bind to antigens, recognised as foreign on a pathogen

Slower:

There are millions of different types of lymphocyte each with a different receptor, there’s only a few of each so not enough to overcome an invasion so specific lymphocytes need to divide by mitosis to produce large numbers of clones (clonal expansion) this takes time.

Describe cell mediated immunity?

This type of immunity involves t-lymphocytes
t cells only respond to nonself antigens which are attached to a body cell
such as: phagocytes, cancer cells

What are the cells called when they can display the antigens of non self antigens on their surface?

Antigen presenting cell

Describe what the types of T cell does (3 roles)

T helper cell: Secrete cytokines (signalling molecules) which stimulate phagocytosis / B-lymphocytes to divide by mitosis
T cytotoxic cell: Secrete hydrogen peroxide to destroy body infected cells, they are the only cells able to detect and destroy pathogens hiding in your body cells, not in the blood or tissue/lymph fluid
T memory cell: remain in the body for many years, this provides long term immunity.

Describe humoral immunity?

this immunity involves B-lymphocytes
Plasma B cells produces antibodies
different shaped antibodies are produced by different B cells
B cells have surface receptors that are the same shape as the antibody that they make
surface receptors are complementary to specific antigens

Explain the entire process of humoral immunity involving B lymphocytes

Clonal selection - Pathogen’s antigen presented to B-lymphocytes
Antigen binds to comp receptor on cell surface of B-lymphocytes

Clonal expansion - B-lymph reproduces by mitosis
produces B-lymph clones

Differentiation - B-lymphocytes differentiate into plasma cells which secrete antibodies specific to pathogen’s antigen
OR B-memory cells which remain in the body for many years, forms long term immunity

Immunological memory - Large number of clones (memory cells) of B-lymphocytes with specific receptor to antigen
quicker clonal expansion
more clones differentiate
more plasma cells, more antibodies secreted into the blood.

Explain the entire process of cell mediated immunity involving T lymphocytes

Clonal selection - APC/infected cell presents antigen
Antigen binds to comp receptor on cell surface of T helper cell

T-lymphocytes reproduces by mitosis
produces T-lymphocytes clones

Differentiation - T-lymphocytes differentiates into
T-helper cells which secrete cytokines which stimulates phagocytosis/B-lymphocytes to mitosis
T-cytotoxic cells secrete hydrogen peroxide to destroy body’s infected cells
T-memory cells which remain in the body for years, creates long term immunity

Immunological memory - Large number of clones (memory cells) of T-lymphocytes with specific receptors to antigen.
quicker clonal expansion
more clones differentiate
more t-helper cells to stimulate mitosis in B-lymphocytes
more t-cytotoxic cells to destroy infected cells.

What are monoclonal antibodes?

Antibodies made from a hybridoma which all the antibodies are the same

Describe the structure of an antibody

They are proteins
They are made up of 4 polypeptide chains, 2 long, heavy chains
2 short, light chains
the variable region is specific to an antigen
it has disulphide bridge polypeptides together

What is aggutinlation?

antibody causes microbes to stick together

What is a vaccine?

Contains an antigen that stimulates the production of antibodies