Alevel Biology

Name the bond found in carbohydrates

glycosidic

What is a polymer?

A molecule made up of many repeating subunits

Name the bond that holds two monosaccharides together to form a disaccharide?

Glycosidic

Name the products of the reaction between glucose and fructose?

Sucrose and water

How does α -glucose and β-glucose differ?

The OH and H are inverted on Carbon-1

Give a feature of the structure of glycogen and explain how that feature helps the function of glycogen.

Branched - lots of terminal glucose for rapid hydrolysis and energy release. Insoluble - don't leak from cells (good for a storage compound) and don't cause water to move in and out of cells.

Why does glucose taste sweet but starch does not

Glucose is soluble and can dissolve in saliva and fit into taste receptors on the tongue

What gives cellulose its structural strength?

It contains a lot of H bonds that make the structure very strong

What two molecules are required to turn lactose back into its monomers

Lactase (an enzyme) and water

Give two ways in which structure of amylose is related to its function

Insoluble - doesn't leak from cells or cause water to leave or enter the cells
coiled structure - compact for storage

Outline the test for non- reducing sugars (4)

- Add sample and boil with HCl to hydrolyse the glycosidic bonds of the sucrose.
- Neutralise with sodium hydrogen carbonate.
- Add Benedict's and heat to 95oC.
- Brick red precipitate formed if positive result.

Outline the test for lipids and what a positive result would show. (3)

-Crush
-Add Ethanol
-Add water
-Shake
-White milky precipitate forms

Define an unsaturated fatty acid. (1)

Contains double bond between carbon atoms

Give two differences between a phospholipid and a triglyceride. (2)

Phospholipid has a phosphate group and two fatty acids

Name the bond found in triglycerides (1)

Ester

Outline the structure of cellulose (4)

- B glucose/ every other monomer is inverted/
- forms long straight chains/
- hydrogen bonds form between chains to form microfibrils
- Number of H bonds gives cellulose its structural strength for cell walls

Which two monomers produce the following:
Sucrose
Lactose
Maltose

Glucose + Glucose = maltose
Glucose + Galactose = lactose
Glucose + Fructose = sucrose

Name the reaction that occurs between a glycerol molecule and a fatty acid?

Condensation

Describe why starch is good for storage?

Insoluble in water

Define a quaternary structure protein and give an example

More than one polypeptide chain joined together eg. Haemoglobin

What test could you do to show that an enzyme is present in a solution?

Biuret's test

Explain the effect of pH on enzymes and their action

-pH too high/low disrupts ionic and hydrogen bonds in tertiary structure.
-Bonds break and shape (including active site) changes.
-Substrate no longer able to bind.

Define a tertiary structure protein

Tertiary structure is the further folding of a polypeptide chain due to bonding between 'R' groups (hydrogen, ionic, disulphide bridges). This gives a specific 3D shape

Why are enzymes only specific to one particular substrate

Specific active site that is only complementary to one type of substrate allowing it to bind the active site and form an enzyme-substrate complex.

How can you tell whether a solution contains a competitive or non competitive inhibitor

Solution with competitive inhibitor will see rate of reaction slowed but can be increased by adding more substrate and out-competing inhibitor. Adding more substrate in presence of non-competitive inhibitor will not increase rate of reaction.

Describe the digestion of carbohydrates

Salivary amylase hydrolyses starch into maltose, which is then denatured in stomach. Pancreatic amylase continues this in small intestine then maltase hydrolyses maltose to glucose

Give 3 ways in which the structure of DNA is related to its function

Long - stores lots of information.
Stable double helix - protects information.
Weak hydrogen bonds - can unravel for replication or transcription.

Name the four bases found in DNA?

Adenine, cytosine, guanine, thymine

How does a non competitive inhibitor work?

Binds to allosteric site, alters tertiary structure including active site permanently. Substrate can no longer bind to active site.

Name the two enzymes involved in DNA replication and their function.

-DNA Helicase breaks the bond between the bases unzipping the double stranded molecule
-DNA polymerise joins the nucleotide together to form the sugar phosphate backbone

Explain the role of endopeptidases and exopeptidases in protein digestion

Endopeptidases hydrolyse peptide bonds in the middle of polypeptide chains, exopeptidases hydrolyse peptide bonds at then end of polypeptide chains

What is the role of hydrochloric acid in the stomach

Kill bacteria

Three benefits of using immobilised enzymes

-Continuous process
-Don't have to be separated from product
-Enzymes reusable
-Enzyme more stable
-Avoid end-product inhibition.

What is the function of the rough endoplasmic reticulum?

Protein synthesis

Four differences between an animal and plant cell

Plants cells have:
-Vacuole
-Starch grain
-Chloroplast
-Cell wall

Give four differences between a eukaryotic and prokaryotic cell

Prokaryptic cells have:
-Mesosome
-Cell wall made of murein
-Plasmid
-Slime capsule
-Pilli

What is the role of the mesosome?

Respiration

Tell us four things you know about the nucleus

-Contains DNA
-Controls cell activity
-Surrounded by a nuclear envelope that has pores to allow movement of substances into and out of the nucleus
-The most dense organelle

Give two properties of a fungal cell

-Cell wall made of chitin
-No chloroplasts so no photosynthesis
-Can be unicellular or multi cellular

Why would a cell that produced a lot of a mucus (contains a lot of protein) have a lot of ribosomes?

Mucus contains protein and ribosomes are the site of protein synthesis

What are ribosomes made up of?

Proteins and RNA

Why are new DNA strands formed in the 5'-3' direction?

-DNA polymerase is an enzyme
-So is specific to the 3' end of strand
-5' and 3' ends have different shape

Explain how you would collect a sample of nuclei during cell fractionation

1) Open cell using blender
2) Filter to remove unwanted cell debris
3) Use ice cold, isotonic, buffered solution.
4) Spin the sample in a centrifuge on a low speed.
5) The pellet collected should be the nuclei as they are the most dense.

State the functions of the smooth endoplasmic reticulum

Synthesis and transport of lipids

What are mark points used to identify prophase

1) Nuclear membrane begins to break down
2) Centrioles move to opposite poles of the cell and produce spindle fibres
3) Chromosomes condense and become visible

Name the substance found in the cell wall of
a) plants
b) fungi
c) prokaryotes.

-Cellulose
-Chitin
-Murein

Explain what happens during interphase.

-During G1, the cell grows considerably in volume but continues its normal activity
-During the S phase (synthesis), DNA replication takes place via semi-conservative replication.
-During G2, the cell is preparing to divide. The cell produces more organelles and ATP in order to prepare for division.

What substances are able to pass through the membrane via simple diffusion

-small, lipid soluble, uncharged particles
-i.e carbon dioxide and oxygen

Why do you need to ensure the specimen is thin when doing a root tip squash

To allow light pass through and enable the cells to be seen under the microscope

What is a gene

A section of DNA that codes for a particular protein

Describe the structure of the cell membrane

-Phospholipid bilayer
-Hydrophilic heads
-Hydrophobic tails
-Intrinsic or extrinsic proteins
-Cholesterol in the bilayer
-Glycoproteins / glycolipids

What happens during anaphase?

1. Spindle fibres contract,
2. Sister chromatids are pulled apart

How would you work out the magnification of an image using the scale bar?

Measure the image size of the scale bar and convert to the same units as the actual size
Divide the image size by the actual size

Three differences between an SEM and TEM

SEM- 3D, High resolution external structure
TEM- 2D, higher resolution, internal structure

Explain how molecules move via facilitated diffusion

a) Through carrier/channel proteins
b) From a high concentration to a low concentration
c) Passive process.

How is DNA related to its function

- Long molecule - can store lots of information
- Stable so can pass from generation to generation
- Sugar phosphate backbone provides protection to the bases
- Every three bases codes for an amino acid
- Weak H bonds between the double strand can easily be broken to allow DNA replication to occur
- Helical shape allows it to be compact

How do bacterial cells divide?

- By binary fission
- Cell elongates and DNA replication occurs
-Cell wall and plasma begin to divide
-Cross wall forms completely around divided DNA
-Cells separates.

Describe the stages of phagocytosis

1) Toxins draws pathogen towards the phagocyte
2) Phagocyte engulfs the pathogen
into a vesicle
3) A lysosome fuses with the vesicle to form a phagolysosome
4) Digestive enzymes from the lysosome hydrolyse the pathogen
5) Waste products are excreted from the cell via exocytosis
6) Pathogenic antigens displayed on the surface

Give two ways in which drugs can prevent uncontrolled cell division

-By preventing DNA replication
-By preventing spindle fibre formation and metaphase

Describe how glucose is absorbed by co-transport (3)

a) Na+ ions move from cell into the blood stream via active transport
b) Glucose moves into the bloodstream via facilitated diffusion
c) This lowers the concentration of both inside the epithelial cell.
d) Na+ now moves into the cell from the small intestine via facilitated diffusion
e) Glucose co- transported into the cell with the Na+ from the small intestine

How would you separate amino acids within a protein?

-Using chromatography and work out Rf values of each amino acid to identify

How are proteins digested?

1) Proteins digested firstly by pepsin in the stomach (endopeptidases)- these break up polypeptides in the middle
2) Then endo- and exopeptidases in the small intestine break down the smaller polypeptides into dipeptides
3) Dipeptidases hydrolyse dipeptides into amino acids which can then be absorbed into the bloodstream

What is a vaccine?

- Dead or weakened form of the pathogen
- With antigens on its surface that stimulate an immune response to allow for the production of memory cells and antibodies for a secondary response.

Give two ways in which monoclonal antibodies can be used in medicine

- Cancer treatment - antibody binding site is complementary to tumour markers and brings drug directly to cancer cells so reducing impact on healthy cells
-Pregnancy test- antibodies for Hcg hormone are in the test. If urine contains hormone, it binds with antibodies that then indicate positive result

What happens during anaphase?

1) Spindle fibres contract
2) splitting the centromere and pulling sister chromatids to opposite poles of the cells

What are differences between the primary and secondary response?

The secondary response is faster and more extensive

Define an antigen

- A protein on the surface of a cell
- That stimulates an immune response

Why is it important to press hard on the slide when you are carrying out the root tip squash practical?

Ensures the specimen is thin enough for light to pass through and there is only a single layer of cells

Give three differences between and competitive and non competitive inhibitor

- Competitive binds to active site, NCI binds to allosteric site
- Competitive inhibitor is a similar shape to the substrate - non competitive can be any shape
- Competitive inhibitor can be overcome with the addition of more substrate, a NCI cannot.
- The active site remains rigid with a CI but a NCI causes it to change shape.

What happens to surface area to volume ratio as an organism increases in size

It decreases

Name the muscle that separates the thoracic and abdominal cavity

Diaphragm

Define:
a) a monoclonal antibody
b) an antigen

- Antibody specific to one particular antigen
- Derived from the same B cell

- A molecule, usually a protein, on the surface of a cell
- That stimulates an immune response

Describe how the alveoli are adapted for gas exchange

- Large number of alveoli and capillaries increase surface area
- Ventilation and circulation maintain a concentration gradient between the alveoli and the capillaries.
- The alveoli are lined with squamous epithelium that is only one cell thick and capillary walls are only one cell thick and so there is only a very short diffusion distance between red blood cells and the alveoli

What are the differences between active and passive immunity

Active- Exposure to antigen, produces memory cells, long lasting and takes time to develop
Passive- No exposure to antigen, no memory cells, short lasting, immediate protection

Why would it be beneficial to do a number of repeats in an experiment

- makes line of best fit more precise
- allows standard deviation to be calculated
- to show spread around the mean

Why would putting honey on a cut get rid of any infection?

- Honey has a lower water potential than the cut
- Water will move out of the pathogen in the cut by osmosis
- Causing metabolic reactions to stop within the bacteria

Describe phagocytosis

1) Pathogen engulfed into a vesicle
2) Lysosome fuses with vesicle
2) Releases enzymes into the vesicle to hydrolyse pathogen
3) Waste products excreted via exocytosis
4) Pathogenic antigens displayed on the surface of phagocyte

What happens during G1 of interphase

- cell doubles in volume
- cell activity continues as normal

What are the two ways in which chemotherapy drugs fight cancer cells?

-prevent spindle fibre formation
-prevent metaphase from occurring

Why is an ice cold solution used during cell fractionation

reduces enzyme activity

What causes oxygen to move into the tracheoles of an insect at rest?

1) Oxygen is used during respiration in the tissues of the insect
2) This lowers the concentration of oxygen in the tissues
3) Oxygen moves into the tracheoles from the outside via diffusion through the spiracles
4) From a high to a low concentration

What is counter current flow

- blood and water flow in opposite directions
- so that concentration gradient for oxygen is maintained
- along the entire gill filament

In terms of Fick's law, explain how an insect is adapted for gas exchange.

- Tracheoles lined with thin epithelium to decrease diffusion distance
- Tissues in the insect are in very close proximity to the tracheoles, reducing the diffusion distance
- Large surface area of tracheoles to increase SA of diffusion surface
- Concentration gradient maintained between the inside and outside of the insect by respiration

Explain the role of T-cells

1) Bind to antigens presented on the surface of self cells/ phagocytes
2) T cells then divide by mitosis
3) Producing T killer and T helper cells
4) T Killer cells destroy cells containing the pathogenic antigen
5) T helper cells activate B cells for the humoral response

What is the humoral response?

Involves B-cells, clonal selection and the production of monoclonal antibodies

In terms of Fick's law, explain how an fish is adapted for gas exchange

- Concentration gradient maintained across the length of the entire gill filament through countercurrent flow of the blood and oxygen in the water
- Gill filaments, lamellae and capillaries lined with epithelium to reduce diffusion distance
- Large number of lamellae (and gill filaments) to increase surface area

Describe how the structure of the artery is adapted to its function

- Thick muscular and elastic wall to allow stretch and recoil to maintain high pressures
- Narrow lumen to maintain pressure
- Lined with smooth endothelium to reduce friction of blood flow

Explain the role of B cells

- Activated by T cells
- Divide by mitosis
- To form plasma and memory cells
- Plasma cells produce antibodies that are specific to the pathogenic antigen

Describe how substances can be transported across the cell membrane

- By osmosis
1. From a high water potential to a low water potential / down a water potential gradient
2. Through water channels

- By facilitated diffusion
3. Channel / carrier protein
4. Down concentration gradient

- By active transport
5. Carrier protein or protein pumps or channel
6. Against concentration gradient
7. Using ATP from respiration

- By phagocytosis/ exocytosis
8. Engulfing by cell surface membrane to form vesicle

Why do we need an isotonic solution during cell fractionation

Stops water moving into or out of the organelle as this would cause the organelle to shrivel or burst

How is the structure of a capillary adapted to its function

1) Lined with endothelial cells - very short diffusion distance
2) Thin endothelial cells- reduce diffusion distance
3) Narrow lumen to maintain pressure for tissue fluid formation
4) They have fenestrations in their walls to allow for the movement of substances between themselves and the tissue
5) Large surface area of capillaries to increase diffusion

What lowers the water potential within the capillary that allows the reabsorption of water at the venous end of the capillary?

Presence of plasma proteins.

Explain how the lungs are adapted for gas exchange

- Large number of alveoli increases the surface area for faster diffusion
- Large number of capillaries increases SA for diffusion
- Capillaries and alveoli lined with squamous epithelium (one cell thick) allows a shorter diffusion distance
- Ventilation and circulation maintain a concentration gradient between the air in the alveoli and the blood

How is a vein adapted to its function?

Wide lumen to reduce pressure
Valves to prevent backflow

What are the two blood vessels associated with the left hand side of the heart?

aorta
pulmonary vein

Describe the pressure changes that occur that cause the opening and closing of the semilunar valves

- Semi lunar valves open when pressure higher in ventricles than in aorta or pulmonary artery - Semi lunar valves close when pressure in aorta is higher than in the ventricles.

How does protein deficiency lead to an increase in tissue fluid

- Low protein diet means there are fewer large proteins left in the capillary
- This means the water potential in the capillary is not lowered sufficiently
- Fluid is therefore not reabsorbed at the venous end and remains in the tissue

What factors affect the rate of diffusion

Temperature
Surface area
Concentration gradient
Diffusion distance

What effect does raising temperature have on an enzyme?

- Increase in kinetic energy causes ionic and hydrogen bonds to break
- This causes the shape of the active site to change
- The substrate is no longer complementary
- Enzyme substrate complexes no longer formed/ enzyme denatured

Describe the process of DNA replication

- DNA helicase separates the DNA strands via breaking the hydrogen bonds between the strands
- The free DNA bases pair up (A-G)(T-C)
- DNA polymerase attaches itself to the 3' end of the template strand
- Joins nucleotides together to form the sugar phosphate back bone