Biology

Why do fish need a gas exchange system?

- they have a small surface area to volume ratio
- they have an impermeable membrane ( gas can't diffuse through their skin)

What is the structure of a fish's gas exchange system?

How does ventilation in bony fish work

1. The mouth opens, increasing volume in the bucal cavity
2. The pressure drops, causing water to enter
- the opercular flap stops water from entering mouth over the gills
3. The mouth closes, the volume reduces and pressure rises so water is forced over the gills
4. The operculum bulges outwards to reduce pressure and then opens, releasing expired water

what is counter current flow

water is drawn over the lamellae them in the opposite direction to the blood: maintains a concentration gradient so diffusion can happen throughout the lamellae

Structure and function of the xylem

Allows water and dissolved minerals to travel up the plant
- made of dead tissue with open ends to form a continuous column
- contains pits to allow movement of water between vessels
- thickened with spiral deposits of lignin to provide support but allow the plant to stay flexible

Structure and function of the phloem

Transports dissolved sugars in the form of sap
- sieve tue elements transport sugars
- companion cells produce atp for active processes
- the plasmodesmata links the cytoplasms of sieve tubes and companion cells

What is the structure of the vascular bundle in the roots

- xylem vessels arranged in an X shape at the centre - allows plants to withstand mechanical forces
- the X shape is surrounded by the endodermis (outer layer of cells which supply water to the xylem vessels)
- the pericycle: an inner layer of meristem cells

What is the structure of the vascular bundle in the stem

- xylem provides support and flexibility to the stem
- phloem is on the outside of the vascular bundle
- a layer of cambium between the xylem and the phloem, containing meristem cells to produce new xylem and phloem tissues

What is the structure of the vascular bundle in the leaf

Forms the midrib and the veins of the leaf
- leaves have a network of veins spreading outwards for transport and support

How do potometers work

The water evaporating from the leaf is replaced by water in a capillary tube
- the movement of a water bubble can be used to determine the rate of transpiration

What factors affect the rate of transpiration

Number of leaves, size/position of stomata, presence of waxy cuticle, amount of light present, temperature, humidity

How does water enter the root

Enters the root hair cells and move into the xylem tissue because the water potential is higher in the soil than in the root hair cells as dissolved substances in the sap lower the water potential

What is the function of root hair cells

They provide a large surface area so minerals can be absorbed via active transport

Symplast pathway

Water enters the cytoplasm via plasma membrane and moves between cells through the plasmodesmata

Apoplast pathway

Water moves through water filled spaces between cellulose molecules and cell walls
- minerals and salts can move through the acoplaste pathway as it does not involve crossing plasma membranes

How does water move through the xylem?

1. Water evaporates from stomatal air spaces and diffuses out of stomata due to water potential gradient from the air spaces to the outside air
2. The water lost from the air spaces is replaced by water from mesophyll cell walls evaporating
3. This lowers the water potential of mesophyll cells so a water potential gradient is created which pulls water from the xylem across the leaf and into the atmosphere *called the transpiration pull*
- the transpiration pull causes negative pressure in the xylem

What is the cohesion tension theory?

The flow of water in the xylem is maintained by:
- cohesion and adhesion of water molecules due to hydrogen bonding
- root pressure - active transport of minerals from the endodermis to the xylem drives water into the xylem by osmosis so water is pushed upwards

What evidence is there for the cohesion tension theory?

- tree trunks decrease in diameter when the rate of transpiration is highest (during the day) because of negative pressure caused by the transpiration pull
- if a xylem vessel is broken and air enters, the tree can't draw water up the vessel as the column of water is broken
-when a vessel is broken water doesn't leak out and air is sucked in: shows that the vessel is under pressure

Adaptations of xerophytes (plants living in dry conditions)

- small leaves to reduce SA for water loss
- densely packed mesophyll and a thick waxy cuticle to prevent evaporation
- hairs and pits to trap most air and lower the water potential gradient
- rolled leaves to reduce the exposure of the lower epidermis to the atmosphere

translocation

1. Sucrose moves into companion cells via facilitated diffusion and is then actively transported into the sieve tubes (lowers water potential in sieve tubes)
2. Water moves from the xylem into sieve tubes by osmosis (higher water potential in the xylem) - this creates hydrostatic pressure
3. Sucrose moves into respiring cells by active transport which lowers the water potential of the cells so water moves into them by osmosis - lowers the hydrostatic pressure
*mass flow of sucrose down the hydrostatic gradient*

Tracer experiment

1. Plants are grown in radioactive CO2 which becomes incorporated into sugars produced in photosynthesis
2. The movement of the radioactive sugars can be traced - the areas close to the phloem (the areas exposed to the radioactivity) are black - this is where the sugars are transported

how is oxygen transported to the tissues in insects

transported in tubes called trachea, which open to the air through holes called spiracles
the trachea run oxygen to different parts of the body, and branch into tracheoles to reach the tissues
- gas exchange happens on the tracheolar lining, which is thin and moist so that oxygen dissolves and diffuses into the cells

why is there water in the the tracheoles

exchange happens where the fluid and the gas meet
- when lactic acid accumulates during activity the water potential is lowered and fluid is drawn out of the tracheoles
- this means that exchange happens closer to the cells

the adaptations of leaves for gas exchange

- stomata to allow gases to enter and exit leaves and maintain concentration gradient by opening and closing (many to keep the diffusion distance short
- air spaces in the spongy mesophyll allow gases to move around the leaves and come into contact with photosynthesising cells
- leaves are wide and flat to create a large sa

How does inhalation work? (5)

1. external intercostal muscles contract (internal relax)
2. diaphragm contracts and flattens
3. the volume of the thorax increases as the ribcage moves up and out
4. the pressure of the thorax decreases
5. air is forced into the lungs

How does exhalation work? (5)

1. external intercostal muscles relax (internal contract)
2. diaphragm relaxes and abdominal organs push upwards
3. the volume of the thorax decreases as the ribcage moves in
4. the pressure of the thorax increases
5. air is forced out the lungs

How are alveoli adapted for gas exchange?

- walls are only one cell thick
- surrounded by capillaries to provide constant blood flow (increase concentration gradient)
- large number - large surface area

Ringing experiment

1. The bark and phloem of a tree are removed to leave only the xylem
2. Over time the tissues above the missing ring swell with sucrose solution and the tissue below dies
proves that sucrose is transported in the phloem because the sugars can't move past the point where it is removed

what is the function of cartilage

supports trachea and bronchi
prevents lung collapse when pressure drops during exhalation

what is the function of ciliated epithelium

moves mucus in bronchi, bronchioles and trachea towards the throat to prevent lung infection

what is the function of goblet cells

secrete mucus to trap bacteria and dust - reduces the risk of infection (lysosomes can digest the trapped bacteria)

what is the function of smooth muscle

can contract to constrict airway and control airflow to and from the alveoli

what is the function of elastic fibres

stretch and recoil during inhalation/exhalation to control airflow

what is a spirometer

measures lung volumes

tidal volume

the volume of air breathed in and out at each breath at rest

breathing rate

the number of breaths per minute

vital capacity

the max volume of air inhaled or exhaled in 1 breath

residual volume

the volume of air remaining in the lungs after exhalation

expiratory reserve volume

the volume of air that can be exhaled in addition to the tidal volume

pulmonary ventilation =

ventilation rate x tidal volume

pulmonary fibrosis

scars thicken the pulmonary epithelium - oxygen can't diffuse into the blood and elasticity is reduced so ventilation is harder
symptoms:
- shortness of breath
- dry cough
- fast, shallow breathing
caused by coal dust, mould, smoking

asthma

allergic reaction releases histamines into bronchi so the lining of the airways becomes inflamed, more mucus is secreted and the airways contract
symptoms:
- wheezing
- difficulty breathing

emphysema

elastic tissue in the lungs (elastin) stretches so lungs can't force air out of alveoli
symptoms:
- blue skin
- shortness of breath
- shallow breathing
- chronic cough
caused by smoking tobacco

tuberculosis

bacterial infection of tubercles in the lungs
symptoms:
- coughing blood
- high temperature
- weight loss
risk factors: overcrowding, poor diet, aids

What are the 5 stages of human nutrition

1. Ingestion: food enters the alimentary canal
2. Digestion: breakdown of complex food into simple absorbable subunits
3. Absorption: the passage of digestion products into the blood/lymph system
4. Assimilation: conversion of absorbed nutrients into complex molecules
5. Egestion: expulsion of un digested/un absorbed materials

Digestive system parts and functions

Liver: makes bile, 'cleans' the blood
gallbladder: stores bile made in the liver, then empties it to help digest fats
large intestine/colon: absorbs water and sodium from the stool
Oesophagus: carries food from the mouth to the stomach
stomach: digestion of protein begins
pancreas: a gland that makes enzymes for digestion and insulin
small intestine: most digestion occurs
rectum: the lower end of the large intestine, leading to the anus
Anus: the opening where bowel movements leave the body

How are carbohydrates broken down?

By hydrolysis of glycosidic bonds

What are the names, locations and functions of the membrane bound disaccharidases

- amylase: in the mouth, breaks down large polymers
- sucrase: in the small intestine, breaks down sucrose
- lactase: small intestine, breaks down lactose
- maltases: found in the ileum bound to microvilli, break down monosaccharides

How are lipids digested

- emulsified into micelles by bile salts to increase surface area and speed up chemical reaction
- lipases in the ileum hydrolyse the ester bond between monoglycerides and fatty acids

How are proteins digested

By peptidases, which are divided into two categories:
- endopeptidases: hydrolyse peptide bonds between specific amino acids at the centre of the polypeptide
- exopeptidase hydrolyse bonds at the end of the polypeptide
- dipeptidases break dipeptides into individual amino acids

proteases are secreted in an inactive form because cells are partly made of proteins, and then activated by HCl in the stomach

How are amino acids and monoglycerides from digestion absorbed by the ileum

Amino acids: facilitated diffusion through surface membrane of epithelial cells
Monoglycerides: are polar, so can diffuse across the cell membrane of epithelial cells

What happens to monoglycerides and fatty acids absorbed by the ileum.

They are transported to the endoplasmic reticulum and reformed into triglycerides
then moved out of cells by vesicles into lymph systems

What is the structure of haemoglobin

- a water soluble globular protein
- two beta polypeptide chains and two alpha helices
- forms a complex containing a haem group
- each molecule carries 4 oxygen molecules bonded to the haem groups

How is oxygen released into tissues?

the greater the partial pressure of oxygen, the greater haemoglobin's affinity for oxygen
- oxygen is used up during respiration, so partial pressure of O2 decreases and haemoglobin's affinity for oxygen decreases
- oxygen is therefore released in to respiring tissues
- 'empty' haemoglobin returns to the lungs, where partial pressure is high, and binds to more O2

What is the Bohr effect?

In high partial pressures of CO2, affinity of haemoglobin for oxygen decreases
- oxygen is released in areas with high respiration rates
- happens because CO2 creates acidic conditions which change the shape of the Hb protein

How does saturation affect haemoglobin's affinity for oxygen?

- after binding to the first O2 molecule the haemoglobin molecule changes shape, and it becomes easier for oxygen to bind to the other haem complexes - *positive cooperativity*
- increased affinity

What does the dissociation curve for haemoglobin look like

- the initial curve is shallow because it is hard for the first O2 molecule to bind
- steep increase as it is easy for molecules 2 and 3 to bind
- the curve flattens as likelihood of 4th O2 molecule finding a binding site is low

Why does Foetal Haemoglobin have higher affinity for oxygen?

The oxygen saturation in the blood is de pleated when it reaches the placenta so the foetus has to survive at a lower partial pressure

What is the closed double circulatory system in mammals

One side of the heart pumps blood to the lungs and the other side to the rest of the body

What order does blood move through the heart?

Vena cava
right atrium
right ventricle
pulmonary artery
lungs
pulmonary vein
left atrium
left ventricle
aorta
body

What is the function of the vena cava

Brings deoxygenated blood back to the heart from tissues

How are the walls of the atria adapted

Thin and elastic so stretch when filled with blood

How are the walls of the ventricles adapted

Thick and muscular to pump blood around the body and to the lungs

What is the function of the aorta

To carry oxygenated blood everywhere but the lungs

What is the function of the pulmonary artery

To carry deoxygenated blood to the lungs

What is the function of the pulmonary vein

To bring oxygenated blood back from the lungs

Myogenic

Can't initiate its own contraction

How does electrical stimulation move through the heart

- the sino atrial node in the right atrium initiates electrical stimulation
- this causes the atria to contract
- the electrical wave reaches the atrioventricular node and is passed through the bundle of His and into the Purkyne fibres
- the ventricles contract

What are the stages of the cardiac cycle

1. Cardiac diastole:
- atria and ventricles relax
- elastic recoil of the heart lowers pressure inside the heart chambers
- blood returns to the heart and fills the atria
2. Atrial systole:
- atria contract, forcing blood into ventricles
3. Ventricle systole:
- ventricles contract
- atrioventricular valves close and semi-lunar valves open
- blood leaves through the heart

Arteries

Carry blood away from the heart
- thick walls to withstand pressure
- elastic tissue and smooth muscle to smooth blood flow
- small lumen to control pressure

Arterioles

Branch of arteries & feed blood to capillaries
- smaller than arteries and have thinner walls

Capillaries

The site of metabolic exchange
- once cell thick for faster exchange of substance
- narrow diameter to slow blood speed

Venules

Larger than capillaries but smaller than veins

Veins

Carry blood towards the heart
- wide lumen to maximise blood flow
- thin walls & low blood pressure
- valves to prevent back flow of blood
- weaker pulse - less need for elastic tissue and smooth muscle

What is tissue fluid

Liquid which supplies tissues with essential solutes in exchange for waste products such as CO2

How is tissue fluid formed?

Hydrostatic pressure is created when blood moves into smaller vessels, so blood fluid is forced out of capillaries
- substances that can move through gaps in capillaries are part of the tissue fluid: amino acids, ions, oxygen, glucose etc.

How does tissue fluid return to the circulatory system

- movs back into capillaries by osmosis
- carried back via lymphatic system

The lymphatic system contains:

- Lymph fluid (similar to tissue fluid but carries waste products
- lymph nodes: filter bacteria and foreign material from the fluid

ionic bonding

association between oppositely charged ions
(negatively charged ions have gained electrons and positively charged ions have lost electrons)

covalent bonding

a type of chemical bond in which two atoms share a pair of electrons (one electron from each atom)

hydrogen bonding

a slightly negatively charged part of a molecule comes into contact with a slightly positively charged part of another molecule
- weak individually but strong in large numbers

properties/ functions of water (5)

- a metabolite (substance necessary for reaction) for many metabolic reactions (condensation & hydrolysis)
- a solvent for reactions
- has a high SHC so buffers temperature changes
- has large latent heat of vaporisation so has a cooling effect when evaporated
- hydrogen bonds cause cohesion between molecules: surface tension and transport in plants

metabolism

the sum of all chemical reactions occurring in an organism

catabolism

breakdown of large molecules to release energy

anabolism

synthesis of large molecules from smaller ones

condensation reaction

two molecules combine to form a more complex one by eliminating a water molecule

hydrolysis reaction

break down of large molecules into smaller ones by the addition of a water molecule

general formula of carbohydrates

Cn(H2O)n

function of carbohydrates

an energy source and structural material in plants

alpha glucose

beta glucose

How are disaccharides formed?

two monosaccharides undergo a condensation reaction to form a glyosidic bond

what is a reducing sugar?

a carbohydrate that is able to donate electrons in chemical reactions
- the carboxyl group gives this property so the anomeric carbon must be free

Where is the anomeric carbon on glucose?

bonded to a OH group and an oxygen

test for reducing sugars

Benedict's test:
- when add to benedict's solution (copper sulphate)
- heat for 3 -5 minutes in a water bath
- a brick red precipitate forms
(because the sugar reduces Cu2+ ions to Cu+ ions, forming copper oxide)

test for non reducing sugars

- use acid hydrolysis to hydrolise the sugars (boil in HCl)
- neutralise the sugar
- do benedicts test (benedicts solution turns from blue to brick red)

what are the three monosaccharides?

glucose, fructose, galactose

sucrose

glucose and fructose

maltose

2 glucose molecules

lactose

galactose and glucose