Organisms exchange with environment

Question 1

Describe the internal structure of a leaf

Answer 1

wax cuticle
thin upper epidermis layer
palisade mesophyll
spongy mesophyll
within mesophyll layers are air spaces
lower epidermis, contains stomata and guard cells

Question 2

Explain how the structure of a leaf is adapted to allow efficient gas exchange

Answer 2

-air spaces within spongy mesophyll, creates a large surface area for gas exchange
-chloroplasts are close to the membrane as vacuole of palisade cells push
-palisade cells are long + thin so large surface area for diffusion
-thin so short diffusion pathway

Question 3

what is a xerophytic plant

Answer 3

a plant living where water is in short supply with adaptions for this condition

Question 4

Explain the adaptions of a xerophytic plant

Answer 4

-thick waxy cuticle to increase diffusion pathway, reducing evaporation
-hairs on leaf to trap water vapor, reducing water potential gradient
-curled leaves reduces surface area, reduces SA:V , increases local humidity so reduces water potential gradient
-sunken stomata to increase local humidity, reduces water potential gradient
-thick stems
-widespread root system

Question 5

Describe the structure of an insects tracheal system

Answer 5

spiracles, trachea, air sac, tracheole, muscle cell

Question 6

Explain how the tracheal system is adapted for sufficient gas exchange in insects

Answer 6

-spiracles so gas exchange can take place through impermeable -exoskeleton
-tracheae are highly branched helping to increase the Surface area : volume ratio available for gas exchange
-trachea straight into muscle cells, increases rate since no time is lost in circulation

Question 7

Explain how the tracheal system of insect balance the need for gas exchange but minimizes water loss

Answer 7

-sunken spiracles
-waterproof exoskeleton that prevents water loss

Question 8

Describe the structure of fish gills

Answer 8

gills on each side of the head
Each gill arch is attached to two stacks of filaments
On the surface of each filament, there are rows of lamellae
The lamellae surface consists of a single layer of flattened cells that cover a vast network of capillaries

Question 9

Explain how fish gills are adapted to maximizing gas exchange

Answer 9

-counter current mechanism-blood and water flows in opposite directions, ensures the concentration gradient is maintained along the whole length of the capillary, water with the lowest oxygen concentration is found adjacent to the most deoxygenated blood
-large surface are due to many filaments
-constant blood supply
-Epithelium covering gills is only one cell thick
-thin lamellea, short diffusion distance

Question 10

Explain the role of cartilage in the trachea and bronchi

Answer 10

c shaped rings for flexibility and strength

Question 11

Explain the purpose of the ciliated epithelial cells in the trachea

Answer 11

cilia are hair like projections captures pathogens + particles
contains goblet cells which produce mucus to trap particles and cilia remove mucus

Question 12

Explain the process of inspiration

Answer 12

External intercostal muscles contract, air enters the lungs, diaphragm contracts/flattens, thorax volume increases, pressure inside lungs is lower than atm pressure

Question 13

Explain the process of expiration

Answer 13

Internal intercostal muscles contact, air enters the lungs, diaphragm relaxes/domes, thorax volume decreases, pressure inside the lungs is higher than atm pressure

Question 14

What is the equation of Ficks Law

Answer 14

Rate of diffusion= (surface area x difference in conc) / length of the diffusion pathway

Question 15

explain Fick’s law in terms of rate of photosynthesis

Answer 15

more co2 = more photosynthesis= more glucose formed= more growth of cell, cellulose

Question 16

Explain the adaption of the tracheal system of an insect in flight

Answer 16

water accumulates at end of tracheole, move in to muscle cells by osmosis during anaerobic respirations, this produces lactic acid which lowers the water potential, gas exchange more efficient as increases concentration gradient for oxygen in air v cells water

Question 17

give brief adaptations of gas exchange surface
* across the body surface of a single-celled organism
* in the tracheal system of an insect (tracheae, tracheoles and
spiracles)
* across the gills of fish (gill lamellae and filaments including
the counter-current principle)
* by the leaves of dicotyledonous plants (mesophyll and
stomata).

Answer 17

• thin so short dp incrs rate of simple diffusion, large sa:vol incr rate across whole body cell
  -spiracles allow o2 to pass through exoskeleton, many tracheoles incr sa
  -counter current incr exchange accross whole length, many lamelle incr sa, thin decr dp
  -spongy mesophyl incr sa, thin short dp, palisade mesophyl long so large sa

Question 18

explain essential features of the alveolar epithelium

Answer 18

· Thin walls - alveolar walls are one cell thick providing gases with a short diffusion distance.
· Moist walls - gases dissolve in the moisture helping them to pass across the gas exchange surface.
· Permeable walls - allow gases to pass through.
· Extensive blood supply - ensuring oxygen rich blood is taken away from the lungs and carbon dioxide rich blood is taken to the lungs.
· A large diffusion gradient - breathing ensures that the oxygen concentration in the alveoli is higher than in the capillaries so oxygen moves from the alveoli to the blood. Carbon dioxide diffuses in the opposite direction.

Question 19

ventilation

Answer 19

ventilation is movement of air in and out of the lungs caused by muscles an active process involves mass flow & flow along air passages;

Question 20

explain full inspiration and expiration

Answer 20

inhalation means air entering
external intercostal muscles contract
diaphragm contracts
thorax volume increases
creates lower pressure in lungs
air enters lungs
air rushes in down air pressure gradient
causing exhalation
diaphragm relaxes
internal intercostal muscles contract moving the rib cage down
abdominal muscles contract during active exhalation; force air out
decreases volume of thorax
raise lung pressure relative to air pressure
elastic recoil of lungs helps exhalation

Question 21

One of the adaptations in some xerophytic plants is a layer of hairs on the epidermis around the stomata. How does this help survival in a desert environment?

Answer 21

moisture is trapped around the stomata -reduces the concentration of the water so less is lost from the leaf/ reduces water potential gradient

Question 22

how to calculate pulmonary ventillation rate

Answer 22

PVR = tidal volume
× breathing rate

Question 23

how to estimate the mean number of stomata in a leaf

Answer 23

1. Get a very thin piece of leaf so that light can pass through and there is only one layer of cells (cells not overlapping)
2. Count the number of stomata in several areas of the leaf so a reliable mean can be calculated and the sample is representative.
3. Record results using stomata per mm2 or cm2 OR Number per mm2 or cm2

Question 24

Xerophytes, what are there adaptions

Answer 24

These are plants that live in habitats where water is in short supply. A thickened waxy cuticle providing a long diffusion pathway and thus reducing the rate of evaporation.
· Hairs on the leaf surface trap water vapour, reducing the water potential gradient for water loss.
· Curled leaves e.g. marram grass, reduces the surface area for evaporation and increases the humidity (water vapour trapped) in the air around the stomata reducing transpiration reducing the water potential gradient for water loss.
· Reduced surface area of leaves reduces SA : vol ratio e.g. pine needles. Fewer stomata, reducing evaporation

Question 25

Asthma
Emphysema.
TB
Pulmonary fibrosis

Answer 25

• Allergic reaction to allergens, muscle surrounding bronchioles contract, narrow bronchi
• Lung damage, caused by inhaling smoke, reduced sa + elestin reducing tidal volume
• disease caused by Mycobacterium, bacteria attack and destroy cells in the alveolar epithelium, leads to scarring/fibrosis, reduces tidal volume.
• fibrosis Scarring of the epithelium often caused by exposure to dust and other airborne particles

Question 26

define digestions

Answer 26

large biological molecules are hydrolysed to
smaller molecules that can be absorbed across cell membranes

Question 27

Explain why the fluid mosaic model is described like this

Answer 27

Fluid- refers to substances able to move laterally, not in a fixed place
Mosaic- refers to the mixture of substances that make up the membrane:
glycoproteins glycolipids (extrinsic proteins), phospholipid layer, carrier proteins and channel proteins (intrinsic proteins), cholesterol

Question 28

Explain function of a phospholipid bilayer

Answer 28

Phospholipids:
Hydrophobic tails (fatty acid chains)
Hydrophilic heads (phosphate groups) point out towards the membrane surface
making layers lipid soluble, wont let water soluble pass
Individual phospholipid molecules can move around within their own monolayers by diffusion

Question 29

Explain the function of cholesterol

Answer 29

Provides stability as it restricts movement since cholesterol molecules also have hydrophobic tails and hydrophilic heads

Question 30

Explain the structure and function of glycolipids and glycoproteins
Extrinsic proteins

Answer 30

These are lipids and proteins with carbohydrate polysaccharide chains attached
Used for cell recognition and communication
These carbohydrate chains project out into whatever fluid is surrounding the cell

Question 31

Explain the structure and function of intrinsic proteins

Answer 31

proteins channel- fills with water to allow water soluble ions to flow through, specific to different ions
carrier protein- used in active transport, requiring ATP, molecules bind and change shape of protein hydrolysing ATP and pushing molecule to other side of membrane with high conc

Question 32

What effect membrane permeability

Answer 32

The amount of cholesterol in the membrane: In eukaryotes, the higher the cholesterol concentration, the lower the membrane permeability
*saturated and unsaturated hydrophobic tails, have kinks making it more permeable
*Temp, higher the more permeability
*Polarity of molecule, faster rate when smaller and no charge

Question 33

How does temperature effect the permeability of membranes

Answer 33

-As temp increases, phospholipids gain kinetic energy causing gaps to appear between phospholipids causing the membrane to become more permeable
High temps cause the proteins in the membrane will denature, increasing the permeability of the membrane
-As temp decreases, freezing forms ice crystals which pierce and break the cell membrane

Question 34

How does ethanol/detergents effect the permeability of membranes

Answer 34

Alcohol and detergents dissolves the phospholipid bilayer causing an increase in membrane permeability

Question 35

Define osmosis

Answer 35

The net movement of water molecules from an area of high water potential to an area of low water potential through a partially permeable membrane, (without the need for ATP, only kinetic energy)

Question 36

Explain the meaning of water potential

Answer 36

The pressure exerted by water molecules
Ψ- symbol

Question 37

Define the terms hypotonic, isotonic and hypertonic

Answer 37

hypotonic- Ψ is closer to zero/ more positive, water enters
isotonic-Ψ is equal on both sides of membrane
hypertonic-Ψ is further from zero/ more negative, shrivels

Question 38

Explain the movement of water into and out of animal and plant cell

Answer 38

Animal: hypo- cell will swell and eventually burst since there are no cell walls to support
Plant: hypo- cell will become turgid since it has a strengthened cell wall

hyper- cell will shrink and shrivel as water leaves the cell

Question 39

Explain simple diffusion

Answer 39

the net movement of molecules from an area of high concentration to an area of low concentration
without the requirement of ATP, only kinetic energy
usually lipid soluble, small molecules, o2, co2,h20

Question 40

Explain facilitated diffusion

Answer 40

A selective process with the use of carrier proteins and channel proteins for molecules that are too big and not lipid soluble.
Channel proteins fill with water to allow certain water soluble ions pass through.
Carrier proteins have specific shapes to allow certain molecules to bind and causes a change in shape to push through other side.

Question 41

Describe Fick’s law

Answer 41

rate of diffusion= difference in concentration x surface area / thickness

Question 42

What effects the rate of diffusion?

Answer 42

-surface area
-size of diffusion pathway
-concentration gradient
-temperature

Question 43

what is active transport

Answer 43

The movement of molecules from an area of low concentration to an area of high concentration with the use of ATP

Question 44

Explain how active transport works

Answer 44

Specific molecule will bind to the inner carrier protein. ATP will bind and will be hydrolysed into ATP + Pi causing the carrier protein to change shape holding onto the Pi. This will push the molecule to the other side of the membrane as Pi is released and protein reverts to original form