Movement of substances - 4th form Flashcards
1
Q
what is diffusion
A
the random movement of particles from an area of higher concentration to an area of lower concentration
2
Q
how do all particles move
A
randomly (in different directions) all the time due to their kinetic energy
3
Q
what does diffusion describe
A
the overall direction and speed of movement
4
Q
what happens to the particles over time in diffusion
A
they will be equally distributed - this is called the equilibrium
—- this does not mean that the particles stop moving!
5
Q
what can diffusion (and osmosis) happen at
A
different speeds or rates
6
Q
what are the four main factors that affect the rate of diffusion
A
temperature
concentration gradient
distance
surface are: volume
7
Q
how does temperature affect the rate of diffusion
A
at higher temperatures, molecules have more kinetic energy and so move faster - therefore diffusion occurs faster
8
Q
how does concentration gradient the rate of diffusion
A
if there is a very large difference in concentration between two areas, molecules will diffuse from the higher to the lower concentration quickly. if the concentration gradient (difference) is small, diffusion will happen more slowly
9
Q
how does distance affect the rate of diffusion
A
diffusion takes longer if the molecules have to travel further. therefore cells are small (smaller volume reduces distance)
10
Q
how does surface area: volume affect the rate of diffusion
A
a larger surface area speeds up the rate of diffusion as there are more oppurtunities for the molecules to move, which is why surfaces such as alveoli in the lungs are so large. surface area to volume ratio is more significant, as the two counteract (oppose) each other: an efficient exchange surface has a surface area which is very large compared to the distance the molecules much travel. SA:V is increased when structures are small
11
Q
what do cells which rely on diffusion for their function typically do
A
maximise their surface area and minimise their volume
12
Q
what is osmosis used to describe
A
the movement of water molecules across a membrane - it is a special type of diffusion
13
Q
what is osmosis
A
the net diffusion of free water molecules from an area of high water concentration to an area of low water concentration across a partially permeable membrane
14
Q
what happens to free water molecules and undissolved sugar molecules
A
when the sugar dissolves water molecules are attracted to the sugar molecules. these water molecules are now not considered free
therefore there are less free water molecules in the beaker
15
Q
what is a partially permeable membrane
A
a membrane that only allows certain particles through
16
Q
what is water potential
A
a measure of the concentration of free water molecules in a solution.
17
Q
what is the water potential in pure water
A
zero
18
Q
what happens to water potential as a solute is added
A
water potential falls as there will be a lower concentration of free water molecules
19
Q
what is the water potential like in concentrated solutions
A
have a very low water potential
20
Q
how does osmosis move water in terms of water potential
A
water moves from an area of high water potential to an area of lower (more negative) water potential
21
Q
what are free water molecules constantly doing
A
moving in and out of cells
22
Q
why do animal and plant cells react differently to being placed in different concentrations
A
plant cells have a cell wall which can withstand a large amount of water pressure
23
Q
what is an isotonic solution
A
the solution outside the cell has the same water potential as inside the cell - no net movement
24
Q
what is a hypotonic solution
A
the solution outside the cell has a higher water potential than inside the cell - net movement of free water molecules into the cell
25
what is a hypertonic solution
the solution outside the cell has a lower water potential than inside the cell - net movement of free water molecules out of the cell
26
what is an animal cell like in a hypotonic solution
lysed
27
what is an animal cell like in an isotonic solution
normal
28
what is an animal cell like in a hypertonic solution
shrivelled
29
what is a plant cell like in a hypotonic solution
turgid (normal)
30
what is a plant cell like in an isotonic solution
flaccid
31
what is a plant cell like in a hypertonic solution
plasmolyzed
32
why do plants wilt
because there is not enough water to fill their cells and therefore the cytoplasm shrinks from the cell wall
33
how is active transport used by organisms
to transport substances against the concentration gradient
34
what does the organism need for active transport
special carrier proteins in the cell membrane. these use ATP to provide the energy to move the substances across the membrane against the concentration gradient
35
what is active transport
the movement of molecules from an area of low concentration to an area of high concentration using ATP
36
what is an example of active transport in humans
glucose is absorbed by active transport in the small intestine
37
what is an example of active transport in plants
plants use active transport in their root hair cells to absorb mineral ions
38
what experiment can be used to demonstrate the relationship between surface area : volume ratio and rate of diffusion
Agar cubes of different sizes
the cubes contain alkali and an indicator - they are placed in an acid. as the acid diffuses into the cube it reacts with the alkali - this neutralisation turns the indicator colourless
the smallest cube becomes colourless quickest
39
what method can be used to determine the water potential of the potato
potato chips can be placed in sucrose or salt solutions of different concentrations
osmosis will occur until the water potential of the tissue and the solution are the same; this causes a mass change
40
in the potato experiment what happens if the solution has a higher water concentration
water will move into the potato chip and the mass will increase
41
in the potato experiment what happens if the solution has a lower concentration
water will move out of the potato chip and this means the mass will decrease
42
what does it mean if there is no change in mass in the potato chip experiment
the concentration of the solution is the same as the concentration of the cytoplasm
43
what could you explore in the potato experiment by leaving it for a short time (e.g 20 mins)
you could explore the effect of concentration gradient on the rate of osmosis
44
what will happen to the potato chips in solutions where the concentration has the biggest difference to the cytoplasm
they will experience the biggest mass changes
45
what is the set up of investigating factors affecting rate of diffusion and osmosis
beaker of water with visking tubing and a capillary tube inside of it which contains sucrose solution
-- the liquid will rise
46
what does visking tubing allow
only allows small soluble molecules to pass through (e.g glucose and water) therefore osmosis can occur
47
what can you do to investigate the effect on osmosis
you could change the concentration of the sucrose solution of the temperature of the water - the height the liquid rises in a set time will increase if osmosis is faster
48
what thing can we use to study the effects of osmosis
thin sections of onion cells
49
what does the transport system in plants enable
enables leaves to receive water for photosynthesis and mineral ions needed to convert the products of photosynthesis into useful substances. once formed these are then transported to other parts of the plants like growing tips, flowers and storage areas
50
features of the xylem
- made up of thick walled dead cells which cotain no cytoplasm - these are completely hollow and arranged end to end
- cell wall contains lignin - waterproof
- the end walls have broken down so they form a continuous transport system throughout the plant
- transports water and mineral ions from the roots to the leaves
- nitrate ions are needed to make amino acids and proteins
- magnesium ions are needed to make chlorophyll
51
what does the cell wall in the xylem contain
lignin - waterproof
52
what does the xylem do
transports water and mineral ions from the roots to the leaves
53
what are nitrate ions needed to make
amino acids and proteins
54
what are magnesium ions needed to make
chlorophyll
55
features of the phloem
- this consists of living cells
- tubes are formed by cells arranged end to end but have cell walls made of cellulose
- the sugar made in photosynthesis is converted to sucrose (another sugar)
- phloem transports sucrose and amino acids from the leaves (where they are made) to the growing points (e.g the tips of the shoot and flowers) or storage areas (such as the roots or bulbs)
- moving sucrose and amino acids around the plant requires energy. this is called translocation
56
what is the cell wall of the phloem made of
cellulose
57
what does the phloem do
transports sucrose and amino acids from the leaves to the growing points or storage areas
58
what is translocation
moving sucrose and amino acids around the plant in the phloem (which requires energy)
59
what do plant take in water from the soil through
their root hairs
60
what is the main site of water absorption by the roots
root hairs
61
describe the root hairs
- they are thin walled (short distance) and have hair like extensions that greatly increase the surface area of the root epidermis
62
what do the hair like extensions in the root hairs do
greatly increase the surface area of the root epidermis
63
what is the concentration of the solutes in the water compared to the solutes inside the root hair cells
the water has some solutes dissolved in it but their concentration is much lower than the concentrations of solutes inside the root hair cells
63
what is the function of the root hair cells
to absorb water and minerals from the soil
64
what are actively transported into the root hair cells
mineral ions
65
what concentration of water molecules does the soil have
higher concentration of water molecules
66
how does water enter the root hair cell
by osmosis
67
where does water move down
water continues to move down a water concentration gradient from where there are more water molecules to where there are fewer water molecules. this gradient is maintained as water is continually being taken up to the xylem in the middle of the root
68
where is water continually being taken up to
the xylem in the middle of the root
69
where is the water carried and where to
carried in the xylem vessels to all parts of the plant
70
what is involved in the movement of water through leaves
osmosis
71
why is the epidermis covered by a waxy cuticle
so it is impermeable to water
72
where does most water pass out of in transpiration
the stomata as water vapour
73
what does water do after it leaves the cells of the mesophyll
evaporates into the air spaces between the spongey mesophyll
74
where does the water vapour diffuse out of in transpiration
through the stomata
75
what does loss of water from the mesophyll cells cause
makes the cells have a lower concentration of water molecules
so water moves into them by osmosis from the surrounding mesophyll cells
76
why does the water leave the xylem in transpiration
replace the water lost from nearby cells
77
what does transpiration cause
causes water to be pulled up the xylem in the stem and roots in a continuous flow known as the transpiration stream
78
explain transpiration
1- most water passes out of the stomata as water vapour
2- water leaves the cells of the mosphyll and evaporates into the air spces between the spongey mesophyll
3- the water vapour then diffuses out through the stomata
4- loss of water from the mesophyll cells makes the cells have a lower concentration of water molecules
5- water molecules moves into them by osmosis from the surrounding mesophyll cells
6- water leaves the xylem to replace the water lost from nearby cells
79
what is transpiration
the evaporation of water from the surface of a plant
80
what are the functions of the transpiration system
- to carry mineral ions to the leaves for the synthesis of amino acids
- to keep turgor pressure high in leaf cells, holding leaves up
- evaporation cools the leaves
-supplies water for photosynthesis
81
what environmental conditions affect transpiration
temperature
humidity
wind speed
light intensity
water supply
82
how does temperature affect transpiration
-on a hot day, water will evaporate quickly from leaves of a plant as the water molecules have more kinetic energy
- transpiration therefore will then increase as temperature increases
83
how does humidity affect transpiration
- very humid air contains a great deal of water vapour --there is a smaller concentration gradient, so transpiration slows down
- in dry air the diffusion of water vapour from the leaf to the atmosphere will be rapid
- transpiration therefore increases if humidity decreases
84
how does wind speed affect transpiration
- in still air, the region around a transpiring leaf will become saturated (full) with water vapour so that no more can escape from the leaf - causing transpiration to slow down
- in moving air the water vapour will be blown away from the leaf as fast as it diffuses out. this will speed up transpiration
- transpiration therefore increases as wind speed increases
85
how does light intensity affect transpiration
- light itself does not affect evaporation, but in daylight the stomata of leaves are open to supply carbon dioxide for photosynthesis
- this allows more water to diffuse out of the leaves and into the atmosphere
86
how does water supply affect transpiration
- if water is in short supply, and the plant is losing water by transpiration faster than it is being taken up by the roots
- then the plant may start to wilt
- before this happens the guard cells become flaccid and stomata start to close, therefore reducing transpiration and delaying wilting
87
what is the stomata
the stomata are holes in the surface of the leaf
88
where are stomata mainly found
mainly found on the bottom surface of the leaf
89
where are the guard cells
there are two cells on either side of the stomata
90
what do guard cells do
they are sausage shaped cells which control the opening and closing of the stomata
91
what does each guard cell have
has a thickened,inflexible inner cell wall (on the stomatal side)
92
what happens to guard cells and stomata in light
they photosynthesise.
- the concentration of sugars increases, the water potential in the guard cells falls and so water moves into the guard cells by osmosis
-they become turgid (swollen) which causes the guard cells to become banana shaped, due to the inflexible inner cell wall, and opens the stomata.
93
what happens to guard cells and the stomata in the dark
photosynthesis stops in the dark
- as the sugar concentration falls (due to respiration), water potential increases and water moves out of the guard cells
- they become flaccid and the stomata close
94
where does the phloem move sugars from and to
from the leaves to other parts of the plant, where they are needed for respiration or growth
95
what is the sieve tube
it is living
it has a thin layer of cytoplasm at the edge of a cell but is mainly filled with sap which flows through the sieve plates and through the phloem
does not have a nucleus and is controlled and supported by neighbouring companion cells
96
describe the translocation of sugars
- the sap flows through the sieve plates and through the phloem
- the neighbouring companion cells have lots of mitochondria and actively transport sucrose into the phloem
- this produces low water potential (due to the high sucrose concentration) and so water moves into the sieve tube by osmosis from nearby cells
- this creates high pressure and pushes the sap towards areas where sucrose (and water) are removed from the phloem
97
what apparatus is used to estimate the rate of transpiration
a potometer
98
how do you set up the potometer experiment
1- the potometer must be set up under water - this prevents any air bubbles from entering the system and blocking the xylem
2- cut the stem of a shoot
3- put the shoot stem into the bung, grease the joint with plenty of petroleum jelly which prevents water loss and air entry
4- put the bung into the potometer
5- make sure the tap is closed and it is full of water (no bubbles). then lift the potometer out of the water
6- leave the end of the capillary tube out of the water until an air bubble forms then put the end into a beaker of water
7- you can measure the transpiration rate as the distance the bubble travels in five minutes. you should take a number of readings and calculate a mean rate
99
what conditions can a potometer be used
to collect readings in normal air, windy conditions, increased temperature, increased humidity and darkness which simulates all the conditions that affect the rate of transpiration
100
what can you do to the leaves in the potometer experiment to demonstrate the importance of the stomata
cover them in vaseline or remove them
101
what is excretion
the removal of toxic waste substances which have been made by cells
102
is the removal of faeces excretion
NO - excretion only applies to materials that are waste products of chemical reactions
removal of faeces is egestion
103
what is a waste product of respiration
carbon dioxide
104
where is carbon dioxide made
respiring cells
105
how is carbon dioxide made
respiration
106
where is carbon dioxide removed
lungs via blood plasma
through leaves in plants
107
where is urea made
liver cells
108
how is urea made
breakdown of amino acids
109
where is urea removed
kidneys and skin
110
explain how urea is formed
1- amino acids are filtered into the liver, along with the rest of the blood via the hepatic artery and hepatic portal vein
2- excess amino acids cannot be stored and need to be broken down so they can be excreted. they are broken down into carbohydrates and ammonia
3- ammonia is very toxic and must be converted into a slightly less toxic chemical called urea
4- amino acids that are needed and the urea are released back into the blood stream via the hepatic vein
111
what does the kidney do
filters the blood and removes any excess materials and passes them to the bladder to be excreted
112
what are the three main sections of the kidney
the cortex - around the outside and a lighter colour
the medulla - in the middle and is triangular shaped
the pelvis - in the centre
113
what are the millions of tiny structures in the kidney called and what do they do
nephrons - structures that filter the blood
114
what are the stages in the filtration of blood
1- ultrafiltration
2- selective reabsorption
3- water reabsorption
115
explain ultrafiltration
1- the diameter of the efferent arteriole at the exit of the glomerulus is smaller than the diameter of the afferent arteriole at the entrance. this creates a build-up of pressure in the capillaries forming the glomerulus.
2- this pressure forces small molecules such as urea, glucose, amino acids and salts out of the capillaries of the glomerulus and into the Bowman's Capsule. This forms the glomecular filtrate
3- larger molecules like protein or red blood cells are too big to fit across the capillary walls and therefore stay in the blood
116
explain selective reabsorption
1- the filtrate travels to the proximal convoluted tubule. however it contains a lot of useful materials such as glucose which would be wasted unless they were recovered
2- there are specialised cells within the walls of the proximal convoluted tube. these move the useful materials back into the blood stream. initially molecules will move by diffusion, but some substances are also moved against a concentration gradient using ATP - this is called active transport
all of the glucose and amino acids are reabsorbed along with some salts and 80% of the water
117
explain water reabsorption
the Loop of Henle and collecting duct are both involved in reabsorbing water if it is needed. the Loop of Henle concentrates the urine by transporting salt into the blood by osmosis
if you have lost a lot of water (through sweating or perhaps haven't taken any in) your body will try and reabsorb as much water from the filtrate as it can. this makes urine very concentrated, with a lower volume of water and therefore it is a darker browner colour.
the collecting duct responds to a hormone called ADH to vary how much water is reabsorbed. this is called osmoregulation
118
photosynthesis chemical equation
6CO2 + 6H2O --> C6H12O6 + 6O2
119
what is the respiration chemical equation
C6H12O6 + 6O2 --> 6CO2 + 6H2O
120
what happens when photosynthesis is faster than respiration during the day, at higher light intensities
there will be a net uptake of carbon dioxide and net release of oxygen. we say oxygen is excreted from the leaves
121
what happens when photosynthesis is faster than respiration in the dark and at low light intensities
there will be a net uptake of oxygen and net release of carbon dioxide. we say carbon dioxide is excreted from the leaves
122
where does gas exchange occur
between the air spaces in the leaves and the atmosphere - carbon dioxide and oxygen diffuse, moving through the stomata
123
how is the leaf specialised for gas exchange
- the leaf is thin, so the diffusion distance is short. it also has a large surface area, increasing the number of stomata, so that carbon dioxide can diffuse quicker.
- stomata allow gases to diffuse into/ out of the the air spaces of the leaf. this provides a short diffusion distance to the mesophyll cells
- gases include moving into/ out of the leaf include water vapour (lost in transpiration), oxygen (absorbed at night for respiration) and carbon dioxide (absorbed for photosynthesis)
- the guard cells form the stomata and can change shape, altering the size of the stomata
- the stomata close and reduce water loss (and gas exchange). this happens when the plant has lost too much water - the guard cells become flaccid, so the cell walls are not held apart and the stomata shrink
124
explain the gas exchange in plants
- this investigation uses sodium hydrogen-carbonate indicator to show the changes in carbon dioxide in the air surrounding leaves in different light conditions
- leaves of, for example, privet are placed in three of four boiling tubes containing a small volume (2cm^3) of sodium hydrogen carbonate indicator (red/ orange when in balance with atmosphere)
- one tube is placed in bright light, one is wrapped in foil, one is wrapped in tissue paper (weak light) and the tube with dead leaf is also left in bright light. the test tubes are then left for 40 mins.
