section 3: exchange and transport (AS level)

Define surface area

The total area of an organism that is exposed to the external environment

Define volume

The total internal space/capacity of an organism

What is the coronation between surface area to volume ratio and the size of an organism?

As the size of an organism increases the surface area to volume ratio decreases and vice versa

Explain why the surface area of volume ratio decreases when the size of an organism increases

This is because volume increases more rapidly than surface area as size increases

Why is simple diffusion sufficient in single celled organisms?

They have a high service error of one more ratio so diffusion across the cell surface meets their needs

How does the large surface area and small volume benefit the organism?

The large surface area allows for maximum diffusion of nutrients and gases whilst the small volume means a diffusion distance to all parts of the cell is short

as organisms increased in size their surface area to volume ratio decreases what does this mean For the organism?

There is less surface area for diffusion compared to the size of the organism and the greater volume results in a longer diffusion distance to all parts of the organism

The surface area of volume ratio of an organism is related to its metabolic rate. true or false?

True

What is the metabolic rate?

It is the energy expended by that organism within a given period of time

Do small organisms with a high surface area to volume ratio, lose more or less heat to their surroundings?

They lose more heat to their surroundings meaning they need a relatively high metabolic rate to maintain body temperatures

Do large animals with a low surface area of volume ratio lose more or less heat to their surroundings?

They lose less heat meaning they can maintain body temperatures at a relatively low metabolic rates

Why does effective gas exchange need to take place?

In order to supply oxygen for respiration and to remove waste carbon dioxide

How do single cell organisms carry out gas exchange?

They carry our gas exchange at the cell surface by simple diffusion

Describe gas exchange in single cell organisms

The high surface area volume ratio means that diffusion occurs as a high rate over their relatively large surface area and diffusion distance from surface to all parts of the cell is short

How does gas exchange take place in insects?

Occurred via tracheal system

Describe gas exchange in insects

Air enters the bodies of insects via openings in the exoskeleton known as spiracles

Air flows into tracheae tubes and then into narrow tubes called tracheoles

Many tracheoles lead to the muscle fibres where their endings provide a large surface area to gas exchange

The movement of gases in the tracheal system mainly relies on diffusion gradient; Oxygen moves down its concentration gradient from the air into its respiring muscle cells and carbon dioxide move down its concentration gradient from the respiring muscle cells into the air

What may active insects need more of?

A more rapid supply of oxygen which they gain using rapid contractions of the abdominal muscles to Draw oxygen into the trachae Down a pressure gradient

What are fish adapted for?

To extract oxygen from water

What do you fish have to maximise the surf surface area for gas exchange?

They have gills

Where are gills located?

On each side of the head

What is each Gill arch attached to?

Two stacks of filaments

What is found on the surface of each filament?

Rows of lamellae

What is the surface of each lamellae made of?

A single layer of flattened cells

What do lamellae cover?

A vast network of capillaries

How is gas exchange in the gills maximised?

It is maximised by a countercurrent system

Why does the blood in the capillary system flow in the opposite direction to the flow of water as it passes over the gills?

To ensure that the concentration gradient is maintained along the whole length of the capillary

Does the water that enter the capillary have the highest or lowest oxygen concentration?

It has the highest oxygen concentration and this flows adjacent to the blood that is already partially oxygenated

Does the water that exit the capillary have the lowest or highest oxygen concentration?

It has the lowest and it is adjacent to the most deoxygenated blood

What do plants need oxygen for?

Respiration

What do plants need carbon dioxide for?

Photosynthesis

What are some adaptations of plant leaves that maximise the exchange of gases?

The spongy massive layer: airflows into and around the air spaces. The surfaces of the spongy mesophyll cells come into contact with the airspaces creating a large surface area for gas exchange

The stomata: These are paws on the underside of most leaves which allow air to enter and exit the leaf. God cells control the opening and closing of the stomata

The shape of the leaves: The leaves are flat and thin reducing diffusion distance for gases

How do you gases move through the cell?

They move in and out of the cells of the leaf by diffusion down their concentration gradient

What is the trade-off between adaptations for gas exchanging water loss?

Adaptations that increase the rate of gas exchange also tend to increase water loss. Therefore, organisms must balance maximising gas exchange with minimising water loss

Describe terrestrial insects

→ insects have a waterproof exoskeleton that prevents water loss by evaporation but the spiracles provide openings through which water vapour can be lost

→ insect features that minimise water loss include the ability to close spiracles and hair around the spiracles to reduce diffusion of water vapour

Describe xerophytic plants

→ Plants need to keep the stomata open to allow gas exchange to occur but opens the matter also allows the loss of water Vapour

→ Plants that live in conditions where freshwater is limited have evolved adaptations to conserve water including few stomata, stomata that are in pits, hairs that are around the stomata, Needle shaped leaves with a reduced surface area and a thickened waxy cuticle

What are some adaptations in cacti that reduce water loss?

Leaves reduced to spines to reduce surface area for water loss

The stem has a thick cuticle to prevent water loss

Where is Maram grass found?

Found on sand dunes

How are the leaves of Maram grass adapted for water loss?

Leaves can Roll up To reduce the exposure of surfaces to the wind

The rolling of the leaf provide deep grooves which protects the stomata

The exposed surface has no stomata And a thick cuticle

The inner surface of the leaf possesses a large number of hairs

What structures does the human gas exchange contain?

The alveoli, Bronchioles, Bronchi, Trachea and the lungs

What is the alveoli?

A series of tiny sacs With structural adaptations that maximise gas exchange. It is the site of gas exchange in the lungs

What are the bronchioles?

Narrow tubes that connect the alveoli to the bronchi

What is the bronchi?

A pair of tubes that connect the bronchioles in each lung to the trachea

What is the trachea?

The airway or windpipe that connects to bronchi with the mouth and nose

What are the lungs?

Two lungs in the chest cavity of the organs of gas exchange

What are all the organs in the gas exchange system?

The nasal cavity, Trachea, Pleural cavity, lung, External and internal intercostal muscles, bronchus, ribs, diaphragm, bronchiole and alveoli

What equipment should use when dissecting?

Scalpel, Dissecting scissors, Tweezers/forceps, Dissecting pins

What is a scalpel?

A sharp blade used for precise cutting

What are dissecting scissors?

Small, sharp scissors used for lower precision Tasks or separating layers of tissue

What are tweezers/forceps?

Useful for manipulating the specimen during dissection

What are dissecting pins?

May be useful for pinning sections of a specimen in place while working

What safety should be taken into consideration during dissection practical work?

→ a lab Coat, Gloves and eye protection should be worn to avoid contamination with biological material

→ Sharp clean blades should be used for eased and accuracy of cutting

→ Scalpel blades should cut away from the body

→ fingers should be kept away from the blade edges

Give a responsible use of biological material

Any biological specimen used for dissection should be from a reputable source and should be disposed of in the correct manner

When dissecting mammalian Lungs, what are key structures that could be seen?

• Trachea supported by C shaped rings of cartilage; Scissors may be needed to cut through the tough cartilage of the trachea

• Bronchi branching into each lung

• Bronchioles

→ structure such as the alveoli can be harder distinguish in a dissecting lung though the spongy texture of lung tissue indicates that lungs contain many air filled sacs

on a fish where are the gills located?

Located on either side of the head beneath a bony flap known as the operculum

When dissecting bony fish gills What are the key structures which can be seen?

• The Gill arch; This can be caught to remove the gill from the fish

• The gill Filaments; Which have a feathery appearance

→ The lamellae Are too small to view by eye but can be examined under a microscope

How can you dissect an insect tracheal system?

1. Attach the insight to a dissecting board using pins

2. Cut the exoskeleton along the length of the abdomen

3. Add a saline solution to the abdomen to highlight the location of the trachea which will show as silvery tubes

→ trachea can me removed and viewed under a microscope

Describe the mammalian gas Exchange tissue

• Alveoli that defer in size and shape

• Alveolar walls that are one cell thick and made up of flattened cells

• Nuclei that are shown as dark clots

• Blood vessels in between the alveoli

Describe the fish gas exchange tissue

• The gill arch Which provides a backbone for the gill filaments

• Many filaments arranged along the Gill arch

• Lamellae visible at higher power

Describe insect gas exchange tissue

→ electron microscopes can take clear images of insect gas exchange structures e.g. the spiracles

Describe the features of dicotyledonous leaves

• Waxy cuticle

• Epidermal layers

• Palisade mesophyll layer

• Spongy mesophyll layer

• Stomata

• Guard cells

How can the volume of air involved in gas exchange be measured?

Using a respirometer, an experimental set up that measures oxygen uptake in living organisms

What do respirometers Measure?

The measure changes and air pressure inside a container; as oxygen is consumed, the air pressure decreases causing a drop of coloured liquid to move towards the region of lower pressure

The distance moved by the coloured liquid in a given time can be used to calculate The volume of oxygen consumed

What do respirometers contain that aid their function?

Three way tap and manometer

What is a three-way tap used for?

Can be opened to allow air into the respirometer altering the internal pressure

This enables the return of the liquid bead to the starting point to allow easy repeat readings

What is a manometer and how is it used?

A narrow tube that contains liquid used to determine the difference in air pressure between 2 sealed containers

The liquid in the tube is drawn towards the container where the pressure is lowest and the distance moved by the fluid can be used to calculate the volume of gas removed

What is the alveolar epithelium?

Functions as a gas exchange surface; CO2 and O2 are exchanged between the alveoli and the capillaries in the process of diffusion

What are some adaptations of the alveolar epithilium that make it an effective gas exchange surface?

A large surface area, thin walls and a steep concentration gradient

How does the large surface area of the alveolar epithilium make it an effective gas exchange surface?

The lungs contain many alveoli increasing the surface area available for O2 and CO2 to diffuse

How do the thin walls make the alveolar epithelium an effective gas exchange surface?

The walls of the alveoli are one cell thick

Alveolar epithelium cells are flattened in shape

Gases have a very high diffusion distance

How does a steep concentration gradient make the alveolar epithelium an effective gas exchange surface?

The constant flow of blood through capillaries that are immediately adjacent to the alveolar epithelium means that oxygenated blood is carried away from the alveoli very quickly

This maintains the conc gradient necessary for diffusion of O2 to occur

How does gas exchange in the lungs occur?

O2 diffuses down its conc gradient from the air into the blood

CO2 diffuses down its conc gradient from the blood into the air

How are the conc gradients required for effective gas exchange maintained?

Ventilation in the lungs and the continuous flow of blood in the capillaries

What is ventilation?

The process of moving air in and out of the lungs and this involves breathing in/inhalation and breathing out/exhalation

Describe what happens when we breathe in

1. The diaphragm contracts and flattens and the external intercostal muscles contract

2. The ribcage moves upwards and outwards

3. Chest volume increases resulting in a pressure decrease in the thorax/ lungs/ thoracic cavity

4. Air moves into the lungs down a pressure gradient

Is the process of breathing in an active or passive process?

Active and therefore it requires energy for muscle contractions

describe what happens when we breathe out

1. The diaphragm relaxes and curves upwards and the external intercostal muscles relax

2. The rib cage moves downwards and inwards

3. Chest volume decreases resulting in a pressure increase

4. Air moves out of the lungs down a pressure gradient

Is breathing out an active or passive process?

Passive process that occurs due to the elastic recoil of the lung tissue

However during forced exhalation the process can become active:

• Internal intercostal muscles contract to pull the ribs down and the abdominal muscles contract to push organs upwards against the diaphragm

• These actions decrease the chest volume further increasing the pressure and for king more air out of the lungs

What is the pulmonary ventilation rate?

Volume of air an individual breathes per minute

What is tidal volume?

The volume of air inhaled or exhaled in one normal breath

What is breathing rate?

The number of breaths taken per minute

How do you calculate pulmonary ventilation rate?

PVR= tidal volume x breathing rate

What are the units for PVR, tidal volume and breathing rate?

PVR= cm3/min

Tidal volume= cm3 or mL

Breathing rate= breaths per minute

What is the effect of lung disease?

Reduces the lung function

What is lung cancer?

When tumours develop in the lungs due to uncontrolled cell division

The tumour may interfere with the normal working of the lungs e.g. by squeezing against blood vessels or blocking airways

What is COPD?

COPD causes damage to the lungs or airways reducing airflow and/or the rate of gas exchange

Range of conditions such as chronic bronchitis and emphysema

What do cigarettes contain?

Cancer causing chemicals

Chemicals that affect the ability to blood to transport

Chemicals that increase mucus production in the airways

What has air pollution been linked to?

Worsened COPD

asthma

Lung cancer

What is a risk factor?

Any factor that is linked to an increased probability of suffering from a particular condition or disease

What are the risk factors for lung disease?

Smoking

Air pollution

Exposure to certain chemicals at work

Genetics

Asthma

What considerations should be taken into account when analysing data from studies on risk factors?

Control variables- it is difficult to eliminate the effects of other variables e.g. diet, activity levels and genetics on the outcome of a study on a specific lifestyle factor

Sample size- the number of individuals in a study needs to be large enough to represent the population as a whole

Sample demographics- the sample needs to contain individuals who represent the target demographic

Correlation vs causation- risk factor data tends to rely on correlation and does not always indicate a casual relationship

Statistical tests: statistical testing should be used to determine whether any associations between variables are significant or due to chance

What is correlation?

An association between variables

What is a positive correlation?

As one variable increases so does the other

What is a negative correlation?

As one variable increases the other decreases

What are casual relationships?

Present when a change in one variable is caused by a change in the other

Is correlation equal to causation?

No; the 2 variables may be linked by a third factor that has not been taken into account by the research

What must researches do to demonstrate that a correlation indicates a casual relationship?

• See the same results repeated across many studies

• Demonstrate that the casual factor is occurring before the resulting change

• Demonstrate the casual mechanism

• Carry out control trials

What is the human digestive system?

An organ system that contains a series of organs that work together to digest and absorb food

What is the function of the mouth an salivary glands?

Food is ingested and teeth break it down into smaller pieces. Saliva is secreted into the mouth. The enzyme begins to digest starch into maltose

What is the function of the stomach?

Protease enzymes begin protein digestion

HCl provides a suitable pH for enzymes and destroys any pathogens in food

What is the function of the liver?

Bile salts are produced here

Bile salts aid the digestion of lipids as well as neutralising stomach acid as it exits the stomach