exchange and digestion+absorption (topic 3)

Question 1

exchange in single celled organisms

Answer 1

can survive with just simple diffusion (short diffusion distance)

Question 2

exchange in multicellular organisms

Answer 2

require specialist exchange surfaces for efficient gas exchange of O2 and CO2

Question 3

features of efficient gas exchange

Answer 3

large surface area
thin (short diffusion distance)
ventilation AND good blood supply / transport system (to maintain a steep concentration gradient)

Question 4

gas exchange in insects 1 - spiracles

Answer 4

spiracles->trachea->tracheoles

gases in/out through tiny pores called spiracles
may be opened or closed by a valve
insects can close them to prevent water loss, and open them to allow gas exchange

Question 5

gas exchange in insects 2 - tracheal system (and maximising gas exchange when active)

Answer 5

relies on diffusion to exchange gases between environment and the cells

tracheae have rings of chitin to keep them open
tracheae branch into tracheoles to increase SA
and shorten diffusion distance (so that cells are always near to the tracheoles)
- tracheoles have thin walls so the diffusion distance is short
- tracheoles have fluid filled sacs (water)
during activity it would move by osmosis into the cell (because anaerobic respiration occurs and lactic acid is accumulated in the muscle cells and lowers the water potential), so more gaseous o2 can fill the tracheoles when needed (faster diffusion)

Question 6

gaseous exchange system in fish - describing gills

Answer 6

gills: protected by a bony plate called operculum
- consist of bony gill arches each with 2 stacks of gill filaments
- these filaments have many protrusions positioned at right angles called gill lamellae

lamellae increase the surface area
they have a thin epithelium that cover a vast network of capillaries so the diffusion distance is short

Question 7

gaseous exchange system in fish - ventilation

Answer 7

• mouth opens and operculum shuts
• floor of buccal cavity (means mouth) lowered
• water enters due to decreased pressure and increased volume
• mouth closes and operculum opens
• floor is raised which decreases volume and increases pressure
• high pressure forces water over the gills

Question 8

counter current flow in fish

Answer 8

blood flow through the lamellae is in opposite direction to water flow
this is so that the concentration gradient is maintained (if flow was parallel O2 levels in blood and in water would reach equilibrium at a point)
80% oxygen in water can be extracted

Question 9

human thorax description

Answer 9

lungs:
-> trachea
. supported by cartilage rings, prevents lungs collapsing in pressure drop in exhalation
. lined by ciliated epithelium (moves mucus along to throat to be swallowed, to prevent lung infection)
. and goblet cells (secrete mucus to trap bacteria and dust, reduces risk of infection with help of lysozymes to digest bacteria)
-> bronchi
-> bronchioles
. smooth muscle is able to contract which constricts the airway and controlling flow of sir into alveoli
-> alveoli

Question 10

alveoli adaptations

Answer 10

• very thin/one cell thick -> reduces diffusion pathway
• large network of pulmonary blood capillaries -> maintains steep concentration gradient
• 300 million in each lung -> increases surface area

Question 11

ventilation: inspiration

Answer 11

external INTERCOSTAL muscles contract, internal relax
causes RIBS to raise up and out
DIAPHRAGM contracts and flattens
therefore VOLUME increases and PRESSURE decreases
difference in atmospheric pressure and inside lungs (pressure gradient) causes air to be forced into the lungs

Question 12

ventilation: expiration

Answer 12

internal intercostal muscles contract, external relax
lowering the rib cage
diaphragm relaxes and raises upwards
volume decreases and pressure increases, forcing air out of the lungs

Question 13

spirometer

Answer 13

measures capacity of lungs:
- breathe in and out of the airtight chamber, causing it to move up and down leaving a trace on a graph.

Question 14

vital capacity def

Answer 14

maximum vol of air that can be inhaled or exhaled in a single breath. varies on gender/age/height

Question 15

tidal volume def

Answer 15

vol air we breathe in and out at each breath at rest

Question 16

breathing rate def

Answer 16

number of breaths per minute
calculated by spirometer trace, number of peaks or troughs in a minute

Question 17

ventilation rate equation

Answer 17

ventilation rate = tidal volume x breathing rate
V
T x B

Question 18

function of the cuticle

Answer 18

contains a waxy chemical to waterproof cells, also prevents gas exchange

Question 19

function of upper epidermis

Answer 19

made from closely packed cells that prevent water from escaping

Question 20

palisade mesophyll function

Answer 20

elongated cells that have a large surface area to enable gases to diffuse in/out (these are the main sites of photosynthesis)

Question 21

spongy mesophyll function

Answer 21

contains air spaces that allow the diffusion of gases

Question 22

stomata function

Answer 22

holes mainly found in lower epidermis that allow gas exchange

• large no of them mean no cell is far from them, reducing diffusion distance

Question 23

guard cell function

Answer 23

found in pairs, control opening of stomata (if they lose water they change shape and close the stomata)

Question 24

xylem function

Answer 24

tubes that bring water to the leaves

Question 25

phloem function

Answer 25

tubes that remove products of PHS from the leaf

Question 26

leaf adaptations for gas exchange

Answer 26

large surface area - thin + flat, lots of area to absorb light for PHS
short diffusion pathway - thin, cells close to stomata
diffusion gradient maintained - o2 used by mitochondria, co2 used by chloroplasts, air spaces in spongy mesophyll

Question 27

structure of stomata and guard cells

Answer 27

guard cells have: cell wall, chloroplasts, vacuole, nucleus

when stomata open, guard cells are swollen/turgid
when stomata closed, guard cells are flaccid due to loss of water

Question 28

plant adaptations to drying out (xerophytes)

Answer 28

• thick waxy cuticle
• reduced surface area of leaves/ make them smaller + thicker
• increase diffusion distance (thicker leaves/more layers of cells)
• reduces water potential gradient by trapping air (sunken stomata, hairs on leaves, rolled leaves)

Question 29

digestion def

Answer 29

the hydrolysis of large INSOLUBLE biological molecules into smaller SOLUBLE molecules that can be absorbed across cell membranes

Question 30

how is the ileum adapted for its function (absorbing products of digestion)

Answer 30

villi -> increases surface area for diffusion
good blood supply -> maintains concentration gradient
epithelial cells one cell thick -> shortens diffusion pathway
epithelial cells covered in microvilli -> increased surface area for diffusion
contain muscle -> able to move and maintain diffusion gradients

Question 31

digestion and absorption of carbohydrates

Answer 31

salivary amylase by salivary glands into mouth. hydrolyses glycosidic bond to form maltose

swallowed into stomach, amylase denatured

small intestine, pancreatic amylase secreted hydrolyses remaining starch to maltose.

epithelial lining produces membrane bound disaccharidase (maltase) hydrolyses maltose -> α glucose

co trasport of glucose (via Na-K pump)

Question 32

digestion and absorption of protein

Answer 32

endopeptidase - hydrolyses peptide bonds between αα in the middle of the protein molecule

exopeptidase - hydrolyses peptide bonds at the ends of a polypeptide

dipeptidase - hydrolyses dipeptides into αα

Question 33

digestion and absorption of lipids

Answer 33

bile salts emulsify large lipid droplets into smaller ones -> increase SA for faster hydrolysis of ester bonds by lipase in triglycerides forming monoglyceride and fatty acids
monoglyceride, fatty acids, bile salts form MICELLES, which make them soluble in water so they can diffuse into the epithelial cell

triglycerides reform in the ER and golgi (modifies them with cholesterol and lipoproteins to form CHYLOMICRONS)
exocytosis - vesicles transporting them and releasing consent outside cell by fusing w/ membrane