All of AQA Uniy 3

What is transpiration?

The loss of water vapor through the stomata of leaves by evaporation

Factors that affect the rate of transpiration

1. Light intensity

- causes more stomata to open

- therefore larger SA for evaporation

2. Temperature

- more heat = more kinetic energy

- so molecules move faster

- therefore more evaporation

3. Humidity

- more water vapour in the air will make the water potential outside the leaf more positive

- therefore reduces the water potential gradient

4. Wind

- more wind will blow away humid air containing water vapour

- therefore marinating water potential gradient

Explain how the structure of xylem tissue is adapted to its function

1. Long tubes w no end walls

- continuous water columns

2. No organelles to obstruct flow

- allows easier water flow

3. Has lignin

- support

- waterproof

4. Pits in walls

- allows lateral movement

Describe the cohesion-tension theory of water transport in the xylem.

1. Evaporation of water molecules through the stomata by transpiration, which lowers the WP of leaf cells

2. Water molecules "stick" together by H-bonds, forming continuous water column

   • these H-bonds maintains column

3. Water pulled up the xylem, creating tension

4. Adhesion of water molecules to walls of xylem

Describe how a high pressure is produced in the leaves.

1. sucrose actively transported in the phloem

2. WP becomes lower as sugar enters phloem

3. Water enters phloem by osmosis

4. Increased volume of water causes increased pressure

What is adhesion in water?

the sticking of water molecules to the xylem wall

- causes capillarity

Explain 2 ways in which companion cells are adapted for the transport of sugars between cells

1. Mitochondria are present to release energy for active transport

2. Ribosomes make proteins which are needed for carrier proteins/enzymes

State and explain the ways in which sieve cells are adapted for mass transport

1. No/few organelles

2. Little cytoplasm

3. Hollow

4. Large vacuole

5. Thick walls

explanation for all:

• easier flow

• stronger resistance to pressure

Describe the mass flow hypothesis for the mechanism of translocation in plants

translocation is how organic materials are transported around the plant

1. In source, sugars are actively transported in the phloem by companion cell

   • this lowers the WP of sieve tube & water enters by osmosis.

2. Increase in pressure causes mass movement towards the sink

3. Sugars used in root for respiration for storage

Give evidence for the mass flow hypothesis of translocation.

1. Cutting the stem of a plant results in phloem sap being released

   • therefore there must be hydrostatic pressure in the sieve tubes.

2. There is a higher sucrose concentration in the leaves than the roots.

Give evidence against the mass flow hypothesis of translocation.

1. The structure of sieve tubes seems to hinder mass flow

2. Not all solutes move at the same speed, as you would expect in mass flow.

How can tracing experiments be used to investigate transport in plants?

• Plants are grown in the presence of radioactive CO2, which will be incorporated into the plant's sugars

- Can determine which tissue carries the radioactively labelled sucrose by:

1. take thin horizontal sections of plant tissue

2. Place against photographic film in dark for several hours and carry out autoradiography

   • we can see that the areas exposed to radiation correspond to where the phloem is.

How can ringing experiments be used to investigate transport in plants?

1. The bark and phloem of a tree are removed in a ring, leaving behind the xylem.

   • Eventually the tissues above the missing ring swells due to accumulation of sucrose and the tissue below begins to die.

- Therefore sucrose must be transported in the phloem.

A student wanted to determine the rate of water loss per mm2 of surface area of the leaves of the shoot.

Outline a method she could have used to find this rate. You should assume that all water loss from the shoot is from the leaves.

1. draw around each leaf on graph paper and count the squares on both sides of the leaf

2. divide the rate of water loss by the total surface area of the leaf

The rate of water movement through a shoot in a potometer may not be the same as the rate of water movement through the shoot of a whole plant.

Suggest one reason why.

plants have roots

What is digestion?

hydrolysis of large insoluble substances to smaller soluble substances

- that can be absorbed through the bloodstream

roles of enzymes in the complete breakdown of starch

• Amylase: hydrolyses starch into maltose

  • by hydrolysing the glycosidic bonds

• Maltase: hydrolyses maltose to glucose

  • by hydrolysing the glycosidic bonds

the process of starch digestion

1. glucose moves into epithelial cell with sodium via carrier protein

2. sodium removed from epithelial cell by AT and moves into the blood, maintaining a low concentration of sodium

3. glucose moves into blood by facilitated diffusion

In a person with a blocked pancreatic duct, starch digestion is affected.

Explain how

blocked pancreatic ducts means that less amylase can enter the small intestine

• so less starch is digested

Healthy people have amylase in their blood. Explain why this doesn’t cause any harmful effects,

amylase is specific to starch

also theres no starch in human blood

Explain how the epithelial cels that line the small intestine are adapted for the absorption of glucose.

1. microvilli which provide large SA

2. many mitochondria which produce ATP

3. carrier proteins for active transport

4. carrier proteins for facilitated diffusion

5. co-transport fo sodium (ions) and glucose

6. membrane-bound enzymes that digest disaccharides, producing glucose

structure of proteins

• proteins are polymer of amino acids joined by peptide bonds, formed by condensation reaction

• primary structure: order of AA

• secondary structure: folding of polypeptide chain due to hydrogen bond

  • forms alpha helix and beta pleated sheets

• tertiary: unique 3D shape formed by the folding of polypeptide chain

  • due to hydrogen bonding, ionic bonding and disulfide bridges

• quaternary structure: 2 or more polypeptide chain

Explain why releasing protein-digesting enzymes into the blood can be harmful the body

these enzymes could digest hormones/antibodies in the blood

Co-transport of sodium and glucose

1. Sodium ions actively transported from ileum to blood

- maintains concentration gradient for sodium

2. glucose enters by facilitated diffusion with sodium ions

Explain why the combined action of endopeptidases and exopeptidases are more efficient that exopeptidases on their own

1. Endopeptidases hydrolyse internal peptide bonds and exopeptidases hydrolyse amino acids at the ends

2. so increase in SA

Role of enzymes in digestion of proteins

1. Hydrolysis of peptide bonds

2. Exopeptidases act at the end of the polypeptide chain

• hydrolyse amino acids at the ends of the chain

3. Endopeptidases act in the middle of polypeptide chain and hydrolyse internal peptide bonds

4. Dipeptidases acts b/w 2 amino acids

Trypsin is a protease.

Suggest the advantage of producing trypsin in an inactive form inside cells in the pacreas

doesnt digest proteins inside the cells

• so pancreatic cells are not destroyed

What are lipids digested by?

Lipase and the action of bile salts

Where is lipase produced and how does lipase digest lipids?

Pancreas and small intestine

Hydrolyses the ester bond in triglycerides to form the monoglycerides and fatty acids

Where are bile salts produced and what do they do?

liver

Emulsify lipids to form tiny droplets called micelles

What are micelles?

water soluble vesicles formed of fatty acids, glycerol and bile salts

describe the action of membrane-bound dipeptidases and explain their importance

• hydrolyses peptides to release amino acids

• amino acids can cross cell membranes, whereas dipeptides cannot cross cell membrane

Explain the advantages of lipid droplet and micelle formation

1. Droplets increase surface areas for lipase / enzyme action

   • So faster hydrolysis/digestion of lipids

2. Micelles carry fatty acids and glycerol through membrane to epithelial cell

Golgi apparatus in lipid transport

1. Modifies lipids

2. Combines triglycerides with proteins

3. Packages them for exocytosis

Digestion and absorption of lipid molecules

1. Micelles contain bile salts and fatty acids

- this makes fatty acids more soluble in water

2. Micelles carry fatty acids to lining of epithelium

3. Fatty acids absorbed by diffusion

When in cell:

1. Triglycerides reform

2. Vesicles move to cell membrane

cooperative binding

• first oxygen binds to haemoglobin, changing tertiary structure

• this creates/uncovers another binding site

• change in shape (of haemoglobin) allows more oxygen to bind easily

How does partial pressure of oxygen affect oxygen-haemoglobin binding?

1.As partial pressure of oxygen increases, the affinity of haemoglobin for oxygen also increases

-so oxygen binds tightly to haemoglobin.

2.When partial pressure is low:

-oxygen is released from haemoglobin.

Bohr effect OxyHb graph

When a high carbon Dioxide concentration causes the oxyhemoglobin curve to shift to the right

The affinity for oxygen decreases b/c the acidic carbon dioxide changes the shape of haemoglobin slightly

Bohr effect

1. As partial pressure of carbon dioxide increases, the conditions become acidic due to the increase in H+ ions, causing haemoglobin to change shape.

2. The affinity of haemoglobin for oxygen therefore decreases

3. so oxygen is released from haemoglobin.and so more oxygen can be delivered to cells for respiration

How does saturation of haemoglobin with oxygen affect oxygen-haemoglobin binding?

It is hard for the first oxygen molecule to bind but once it does:

• first oxygen molecule binds to haemoglobin, changing the tertiary structure

• this reveals/uncovers another binding site

• it changes the shape of haemoglobin to make it easier for the second and third oxygen molecules to bind

• known as positive cooperativity.

It is then slightly harder for the fourth oxygen molecule to bind

• because there is a low chance of finding a binding site.

Explain why oxygen binds to haemoglobin in the lungs.

1. Partial pressure of oxygen is high.

2. Low concentration of carbon dioxide in the lungs, so affinity of Hb to oxygen is high.

3. Positive cooperativity

Explain why oxygen is released from haemoglobin in respiring tissues.

1. Partial pressure of oxygen is low

2. High concentration of carbon dioxide in respiring tissues, so affinity of Hb to oxygen decreases.

if oxyhaemoglobin dissociation curve goes towards the left

• haemoglobin has higher affinity for oxygen

• so it releases less oxygen/ uploads more oxygen

• it becomes saturated at lower partial pressure

if oxyhaemoglobin dissociation curve shifts to the right

• haemoglobin has a lower affinity for oxygen

• so it unloads/dissociates more oxygen, more readily into cells for respiration

  • therefore greater (rate of ) respiration

• at a particular partial pressure, more oxygen released

Foetal haemoglobin

has higher affinity for oxygen (than adult haemoglobin), even at the same partial pressure

• loads oxygen from mothers haemoglobin/blood

• so more oxygen moves from the mother to the fetus

advantage of replacing fetal haemoglobin with adult haemoglobin

• adult haemoglobin has a lower affinity for oxygen

• so more oxygen is released and delivered to respiring cells

• easier unloading of oxygen for aerobic respiration

how oxygen is loaded, transported and unloaded in the blood

1. haemoglobin has a high affinity for oxygen

2. at high partial pressure: oxygen is uptaken into the lungs

3. at low partial pressure: oxygen is released into respiring cells

   • this is due to higher CO2 conc. (bc respiration)

Figure 1 shows the oxygen dissociation curve for human haemoglobin.

• loading of oxygen at high partial pressure

• in the lungs, haemoglobin has a high affinity for oxygen

• haemoglobin unloads oxygen at low partial pressure

Explain how the shape of a red blood cell allows it to take up a large amount of oxygen in a short time.

1. large SA:V ratio

   • for diffusion

2. thin

   • so oxygen can release all haemoglobin

Explain how oxygen in a red blood cell is made available for respiration in active tissues.

• low pH due to increased CO2

• increased dissociation of oxygen from haemoglobin

• oxygen diffuses from rbc to tissues

What is meant by the term partial pressure?

the measure of concentration of a gas

When do the AV valves open and close?

• Open: when pressure is higher in atria compared to ventricles

• Close: when pressure is higher in ventricles than atria

When do semilunar valves open and close?

• Open: when the pressure is higher in the ventricle compared to the arteries

• Close: when the pressure is higher in the arteries compared to the ventricles

role of septum

• separates oxygenated and deoxygenated blood

• maintains high conc. of O2 in oxygenated blood

  • to maintain conc. gradient to therefore enable diffusion at respiring cells

some babies are born with a hole between the right and left ventricles. suggest why these babies are unable to get enough oxygen to their tissues

mixing of oxygenated and deoxygenated blood
- therefore lower volume of oxygenated blood leaves the left ventricle and flows into the aorta

role of tendons

prevents inversion of valves due to high pressure

2 ways in which blood moves in one direction as it passes through the heart

1. blood moves down a pressure gradient

   • blood moves from high to low pressure

   2. valves stop backflow of blood

structure of arteries

1. thick walls: enabling it to carry blood at high pressures

2. elastic tissue: smooths out blood flow and maintains pressure

3. muscles in wall: to control blood flow

4. smooth endothelium: to reduce friction

contrast the structure of arterioles and arteries

• Arterioles have thicker muscle layer than arteries, which contract to control the flow of blood

• Arterioles elastic layer is relatively thinner than the elastic layers in arteries, because blood pressure is lower

why is an arteriole described as an organ?

made up of different tissues/made up of more than one tissue

how do the muscle fibres in arterioles reduce blood flow to the capillaries?

the muscle contracts

• so the arterioles narrows/constricts

• vasoconstriction

structure of aorta

1. elastic tissue: to allow stretching/recoil to maintain pressure

   • elastic tissue stretches when ventricles contract

2. muscles: contraction/vasoconstriction

3. thick walls: to withstand pressure

4. smooth endothelium: to reduce friction

5. SLV: to prevent back flow of blood

suggest why the rise and fall in blood pressure in the aorta is greater than in the small arteries

1. aorta is directly linked to the heart, therefore the pressure is higher in the aorta than in the small arteries

2. aorta has elastic tissue, so it can stretch/recoil

describe the difference in the thickness of aorta wall during each time in cardiac cycle

1. during systole: aorta wall stretches bc ventricles contract
2. during diastole: aorta walls recoil bc ventricles relax

this helps maintain smooth blood flow

explain how the highest blood pressure is produced in the left ventricle

left ventricle has thicker, muscular walls

• therefore stronger contractions

structure of veins

1. thin walls due to lower pressure, therefore requiring valves to ensure blood doesn’t flow backwards

2. less muscular and elastic tissue bc they don’t have to control blood flow

3. smooth endothelium to reduce friction

explain the difference in thickness between pulmonary artery and pulmonary vein

pulmonary artery contains muscle and elastic fibres

• b/c pulmonary arteries handle high pressures and smooth out blood flow

structure of capillaries

1. permeable capillary membrane

2. thin, one-cell thick walls: short diffusion distance/pathway

3. small diameter: short diffusion distance

4. flattened endothelial cells: short diffusion distance

5. numerous and highly branched: provides large SA

6. narrow lumen: reduces blood flow rate to give more time for diffusion

advantage of capillaries being narrow

short distance b/w blood and the outside of the capillary

• therefore fast diffusion

why is the blood flow in capillaries slow?

so that theres more time for diffusion

what factor limits the internal diameter of the lumen of a capillary?

width/diameter of blood cell

how can the widening of blood vessels reduce blood pressure

widening of blood vessels causes larger lumen, which reduces the blood pressure in blood vessels

• therefore less friction/resistance in the blood vessels

suggest why pulse can be used to measure heart rate

pulse is caused by the pressure from one contraction/beat of the heart

role of heart in formation of tissue fluid

1. contraction of ventricles produces high hydrostatic pressure

2. this forces water and some dissolved substances out of the capillaries

how tissue fluid is formed and returned to circulatory system

• high blood/hydrostatic pressure at arterial end of capillary which forces water out

• large proteins remain

• water potential in capillary becomes lower/negative due to these proteins

  • water potential now lower than hydrostatic pressure

• so water enters venous end of capillary by osmosis

• water moves out at the arteriole end and back in at the venule end

• lymph system collects any excess tissue fluid which returns to blood/circulatory system

how does high blood pressure lead to an accumulation of tissue fluid

1. high blood pressure = high hydrostatic pressure

2. increases outward pressure from arterial end of capillary

3. more fluid forced out of capillary due to high pressure

4. so more tissue fluid formed

5. less return of fluid into capillary (due to high pressure)

Explain why a lack of protein in the blood causes a build up of tissue fluid.

water potential in the capillary is higher

- therefore less water removed by osmosis

suggest how an increase in volume of blood entering the heart reduces angina

1. large amount of blood leaves the heart

2. therefore more blood/oxygen flow to the heart muscle via coronary arteries

explain how blood in a vein in the leg is returned to the heart

1. muscles surrounding the vein contracts and press on the walls of the vein, squeezing blood along the veins

2. valves prevent backflow

3. contraction of heart pumpls blood through arteries into vein (systole)

4. the recoil of heart muscle after contraction/ during diastole draws the blood from the veins into the atria

5. veins have wide lumens therefore theres little resistance

how to calculate something with eyepiece graticule

1. measure using eyepiece graticule

2. calibrate eyepiece graticule against stage micrometer

3. take a number of measurements to calculate a mean

Contrast the trachea of a mammal and the trachea of an insect

1. Mammals have just one trachea whereas insects have multiple trachea

2. Trachea of mammals have a larger diameter than trachea of insects

3. Mammal trachea made up of cartilage whereas insect trachea made up of chitin

4. Mammal trachea is longer than insect trachea

5. Mammal trachea branch into bronchi whereas insect trachea branch into tracheoles

Describe the difference in the composition of gases in inhaled and exhaled air.

Explain how these differences are caused.

1. inhaled air contains more oxygen that exhaled air

2. inhaled air contains less carbon dioxide than exhaled air

3. inhaled air contains less water vapour

4. water vapour diffuses from moist surface

5. respiration results in higher blood carbon dioxide and lower blood oxygen

6. oxygen enters blood and carbon dioxide leaves blood in alveoli by diffusion

describe the gross structure of the human gas exchange and how we breathe in and out

trachea, bronchi, bronchioles, alveoli

• 1. when you breathe in: the diaphragm contracts and moves down and the external intercostal muscles contract

  • contraction of diaphragm muscles flattens diaphragm

  • causes an increase in volume and pressure decrease in thoracic cavity (to below atmospheric), resulting in air moving in down pressure gradient

  2. when you breathe out: the diaphragm relaxes and internal intercostal muscles contract

  • diaphragm moves up and becomes dome shaped

  • contraction of intercostal muscles raises ribcage

  • causes a decrease in volume and a pressure increase in thoracic cavity to above atmospheric

  • pressure in lungs is higher than pressure outside

  • resulting in air moving out

apart from reduced elasticity, explain how changes to the lung tissue reduce the efficiency of gas exchange

1. alveolar walls thicken

   • so longer diffusion pathway

2. scarred tissue

   • reduces SA for gas exchange

role of diaphragm in breathing in

1. diaphragm contracts and moves down

2. increases volume in thorax and lowers pressure in thorax

3. air moves in down pressure gradient

   • Reduced pressure allows air to enter

role of diaphragm in breathing out

1. diaphragm moves up and becomes dome-shaped

2. reduces volume of thorax and increases pressure in thorax

3. so pressure in thorax is higher than the outside

how paralysis of diaphragm leads to breathing difficulties

• diaphragm will not contract and move down

• thoracic cavity/lung volume is not increased, so cannot breathe in

movement of ribs when a person breathes in

up and out

explain whether breathing out is active or passive

active because it involves contraction of muscles

three ways in which an insects tracheal system is adapted for efficient gas exchange

1. tracheoles have thin walls

   • so short diffusion distance to cells

2. large number of tracheoles

   • so short diffusion distance to cells

3. large number of tracheoles

   • so large surface area

4. Tracheae provide tubes full of air

   • so fast diffusion into insect tissues

5. Fluid in the end of the tracheoles that moves out during exercise

   • so larger surface area

the structure through which gases enter and leave the body of an insect

spiracle

name the small tubes that carry gases directly to and from the cells of an insect

tracheole

explain the movement of oxygen into the gas exchange system of an insect when it is at rest

1. oxygen used in respiration

2. oxygen moves down a diffusion gradient

The damesfly larva is a carnivore that actively hunts prey. It has gills to obtain oxygen from water.

Explain how the presence of gills adapts the damesfly to its way of life.

• Damselfly larvae has higher metabolic / respiratory rate

• so it uses more oxygen

explain 5 ways in which the structure of fish gills is adapted for efficient gas exchange

1. Gills have many lamellae / filaments so large surface area

2. Thin epithelium surface so short diffusion pathway

3. Countercurrent maintains concentration gradient along gill

   • equilibrium not reached

4. Circulation replaces blood saturated with oxygen

5. Ventilation replaces water as oxygen is removed

counter-current mechanism

1. water and blow flow in opposite directions

2. blood always passing water with a higher oxygen concentration

3. diffusion gradient maintained throughout length of gill/lamella

describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs.

details of breathing are not required.

the oxygen moves through the trachea, bronchi and bronchioles

• down a pressure and diffusion gradient

• across alveolar epithelium and capillary epithelium

how oxygen in the air in the alveoli enters the blood in the capillaries

the oxygen moves by diffusion across alveolar epithelium

Explain why a large number of small alveoli is more efficient in gas exchange than a smaller number of larger alveoli

• small alveoli has larger SA

  • so more diffusion

Forced expiration volume (FEV1) is the volume of air a person can breathe out in 1 second.

One of the severe disabilities that results from emphysema is that walking upstairs becomes difficult.

Explain how a low FEV1 value could cause this disability.

1. less CO2 removed

2. less oxygen uptaken

3. less respiration