Cells Flashcards
(165 cards)
1
Q
Structure of nucleus
A
- nuclear envelope
- nuclear pores
- nucleoplasm
- chromosomes
- nucleolus
2
Q
What is the nucleolus
A
Site of rRNA production and makes ribosomes
3
Q
Function of nucleus
A
- Controlling the cell’s activities - it contains DNA with instructions to produce proteins.
- Synthesis of ribosomes - the nucleolus makes ribosomal RNA.
- Exchange between nucleus and cytoplasm - substances can enter or leave the nucleus via the nuclear pores.
4
Q
Structure of eukaryotic cells
A
- cell-surface membrane
- nucleus
- mitochondria
- chloroplast
- golgi apparatus + vesicles
- lysosomes
- ribosomes
- RER + SER
- cell wall
- cell vacuole
5
Q
RER + SER structure
A
- both have folded membranes called cisternae
- RER have ribosomes on the outer surface but SER don’t
6
Q
RER + SER function
A
RER: provides large SA for protein synthesis + synthesis and transport of proteins
SER: synthesise, store and transport carbohydrates and lipids
7
Q
Golgi body functions
A
- Add carbs to proteins to form glycoproteins
- Produce secretory enzymes
- Process and package lipids and proteins
-> carried out by the cisternae - Store and transport lipids and proteins
-> carried out by the vesicles. - Synthesise lysosomes
8
Q
Lysosomes structure
A
- Contain hydrolytic enzymes
-> digestive enzymes like proteases and lipases, also contain lysozymes - Surrounded by a membrane to keep enzymes separate from the cytoplasm of the cell
9
Q
What are lysozymes and what happens to them
A
- enzymes that hydrolyse the cell walls of certain bacteria
- lysosomes isolate these enzymes from the rest of the cell and then release them either to the outside or into a phagocytic vesicle within the cell
10
Q
Functions of lysosomes
A
- break down material ingested by phagocytosis
- release enzymes outside the cell (exocytosis)
- digest worn out organelles
- completely break down cells after they’ve died (autolysis)
- hydrolyse phagocytic cells
11
Q
Mitochondria structure
A
- double membrane -> inner membrane is folded to form cristae
- matrix
- contain their own DNA and ribosomes
12
Q
What do mitochondria cristae do
A
Provide a large SA for the attachment of enzymes + are involved in respiration
13
Q
What does the mitochondria matrix do
A
Contains proteins, lipids and traces of DNA and also its own ribosomes -> so mitochondria can control the production of their own proteins
14
Q
Mitochondria function
A
- site of aerobic respiration -> produces ATP
- DNA to code for enzymes needed in respiration
15
Q
Ribosomes structure
A
- Made up of 2 sub-units of protein and rRNA
- 80S -> found in eukaryotic cells
- 70S -> found in prokaryotic cells, mitochondria and chloroplasts
- Not surrounded by a membrane
16
Q
Ribosomes function
A
The site of protein synthesis
17
Q
Vacuole structure
A
Filled with fluid surrounded by a single membrane called tonoplast
18
Q
Vacuole function
A
- make cells turgid and so provide support
- temporary store of amino acids and sugars
- the pigments may colour petals to attract pollinators
19
Q
Chloroplasts structure
A
- Contain fluid-filled sacs known as *thylakoids** which are stacked up to form grana
- Surrounded by a double membrane, enclosing a fluid known as stroma
- Contain their own DNA and ribosomes.
20
Q
Chloroplasts function
A
Site of photosynthesis - these reactions take place in the grana and stroma
21
Q
Cell wall structure (plants and fungi)
A
Plants: made of micro fibrils of cellulose polymer
Fungi: made of chitin -> a nitrogen containing polysaccharide
22
Q
Cell wall function
A
- Supports the cell
-> contents of the cell press against the cell wall to make it rigid - Prevents the cell from bursting
-> the cell wall can withstand high osmotic pressure - Allows exchange of substances between cells
23
Q
Cell membrane structure
A
- phospholipid bilayer -> molecules embedded within and attached on the outside
( proteins, carbohydrates, cholesterol)
24
Q
Cell membrane function
A
Controls entry and exit of molecules
25
What things do cell membranes contain
- cholesterol
- glycoproteins
- glycolipids
- proteins
- phospholipids
26
Vacuole structure
- fluid filled sac, bound by a single membrane called a **tonoplast**
- a plant vacuole contains a solution of mineral salts, sugars, amino acids, wastes and pigments such as anthocyanins
27
Function of vacuole
- sugars and amino acids act as temporary food stores
- keeps the cells turgid
- pigments may colour petals to attract pollinating insects
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Object
Material under microscope
29
Image
Appearance of material under a microscope
30
Resolution
The minimum distance apart that 2 objects can be in order for them to appear as separate items
Greater resolution = greater clarity
31
Light microscope
Uses light rays that pass through a specimen and are focused by the objective lens and eyepiece lens to produce an image
32
Light microscope resolution
Have a poor resolution due to the long wavelength of light
33
Transmission electron microscope
Use electromagnets to transmit a beam of electrons through a specimen
-> the denser parts absorb more electrons, so appear darker in the image formed
34
Electron microscope resolution
Better resolution due to a shorter wavelength
35
What are the 2 types of electron microscope
Transmission and scanning
36
TEM Limitations
- whole system must be in a vacuum so living specimens can’t be observed
- a complex staining process
- image may contain artefacts
- only black and white
- specimen must be very thing, resulting in a flat 2D image
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TEM Limitations
- whole system must be in a vacuum so living specimens can’t be observed
- a complex staining process
- image may contain artefacts
- only black and white
- specimen must be very thing, resulting in a flat 2D image
38
Scanning electron microscope
Directs a beam of electrons onto the surface, rather than penetrate it -> has a lower resolving power than the TEM
39
SEM limitations
- whole system must be in a vacuum so living specimens can’t be observed
- complex staining process
- image may contain artefacts
- CAN use thicker specimens
40
Why is cell fractionation possible
Due to the different densities or the organelles
41
What is cell fractionation
Process where cells are broken up and different organelles are separated out
42
What must you do before cell fractionation
Put the tissue in cold, buffered and isotonic solution
43
Why must the solution be cold, buffered and isotonic
Cold - to reduce enzyme activity that might break down the organelles
Buffered - to maintain constant pH as a change in pH could alter the structure of organelles or affect their functioning
Isotonic - to prevent any osmotic gain or loss of water so organelles don’t burst or shrink
44
What are the steps of cell fractionation
1. Place in cold, buffered and isotonic solution
2. Homogenisation
3. Ultracentrifugation
45
What happens in homogenisation
- cells are broken up by a homogeniser -> this releases organelles
- the resultant fluid (homogenate) is filtered to remove any debris + complete cells
46
What happens in ultracentrifugation
- the fragments in the filtered homogenate are separated out in an ultracentrifuge
-> this spins tubes of homogenate quick to create a centrifugal force
47
What speed is the tube spin in ultracentrifugation
- slow at first -> the heaviest organelle (nucleus) is forced to the bottom where it forms a thin sediment or pellet
- the supernatant is removed and spun at a faster speed so the next heaviest organelle is forced to the bottom
48
How does a cell become specialised
Every cell contains genes needed for it to develop into a different cell BUT only some of these genes are switched on (expressed) and the rest of switched off
49
What is a tissue
This is a group of similar cells working together to carry out a particular function
50
Examples of tissues
Epithelial and xylem
51
What is an organ
This is a group of tissues working together to carry out a particular function.
52
What tissues does the stomach have
- muscle to churn and mix the contents
- epithelium to protect the stomach wall and produce secretions
- connective tissues to hold other tissues together
53
What tissues do leaves have
- palisade mesophyll made from palisade cells for photosynthesis
- spongy mesophyll for gaseous diffusion
- epidermis to protect the leaf and allow gaseous diffusion
54
What are the organ systems in animals
Digestive, respiratory and circulatory
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Are eukaryotes or prokaryotes bigger
Eukaryotes are bigger
56
Structure of a bacterial cell
Cell wall - physical barrier that excludes certain substances and protects against mechanical damage and osmotic lungs
Capsule - protects bacterium from other cells and helps groups of bacteria stick together
Cell-surface membrane - controls entry + exit of chemicals
Circular DNA - holds the genetic info for the replication of bacterial cells
Plasmid - holds the genes that may aid the survival of bacteria in adverse conditions
57
Virus structure
(Acellular, nonliving)
- contain nucleic acids (like DNA or RNA) as genetic material -> enclosed within a protein coat called a capsid
- some viruses have a lipid envelope -> the lipid envelope (if present and capsid if not) have attachment proteins that allow a virus to identify and attach to a host cell
58
Prokaryotic and eukaryotic properties
**Prokaryotic**
- no nucleus
- DNA is not associated with proteins
- some DNA may be in the form of plasmids
- no membrane-bounded organelles
- no chloroplasts
- ribosomes are smaller (70S)
- cell wall are made of **murein** (peptidoglycan)
- may have a mucilaginous layer called a capsule
**Eukaryotic**
- have a nucleus with a nuclear envelope
- DNA is associated with proteins called histones
- no plasmids
- membrane - bounded organelles like mitochondria are present
- chloroplasts present in plants and algae
- ribosomes are larger (80S)
- where present cell wall is made out of cellulose (chitin in fungi)
- no capsule
59
What is the cell wall in fungi made out of
Chitin
60
Functions of membranes within cells
- control exit + entry of materials in organelles like mitochondria and cytoplasm
- separate organelles from cytoplasm so specific reactions can take place within them
- provide an internal transport system eg ER
- isolate enzymes that might damage the cell eg lysosomes
- provide surfaces on which reactions can occur eg protein synthesis on ribosomes on the ER
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Structure of cell surface membrane
Phospholipid bilayer
62
What significant about phospholipids
They are polar as they have 2 ends that act differently
63
Function of the phospholipid bilayer in the cell membrane
- allow lipid soluble substances to enter and leave the cell
- prevent water soluble substances from entering and leaving the cell
- make the membrane flexible
64
What 2 ways are proteins embedded in the cell surface membrane bilayer
1. Some are in the surface or partly embedded -> give mechanical support or act as cell receptors
2. Others completely span the bilayer - some are protein channels to transport water soluble molecules across the membrane + others are carrier proteins that change shape and carry molecules across the membrane
65
Functions of proteins in the cell membrane
- structural support
- act as channels, transporting water soluble substances
- allow active transport across the membrane
- act as receptors
- help cells adhere to each other
66
How permeable is the cell surface membrane
Gene really most molecules don’t freely diffuse across it
67
Why don’t molecules generally freely diffuse across the cell membrane
- too large to pass through channels
- not soluble in lipids
- are the same charge as the charge on the protein channels > so are repelled
- are polar > so can’t pass through the non-polar hydrophobic tails
68
What does cholesterol do in the cell membrane
- add strength to the membranes
- very hydrophobic so help prevent loss of water and dissolved ion from the cell
- they also pull the fatty acid tails of the phospholipid molecules -> limiting their movement without making it too rigid
69
Function of cholesterol in the cell membrane
- Cholesterol molecules consist of a hydrophilic and hydrophobic region -> the hydrophobic regions bind to phospholipid fatty acid tails, causing them to pack more closely together.
- So cell membrane is more stable and there's less fluidity -> prevents leakage of water + dissolved ions from the cell
70
What are glycolipids made from
A carbohydrate covalently bonded with a lipid
71
What other components does the cell membrane have
Cholesterol
Glycolipids
Glycoproteins
72
Function of glycolipids and glycoproteins in the cell membrane
1. Cell adhesion - This is the attachment of cells to one another.
2. Cell recognition - This allows cells to recognise one another.
3. Cell signalling - This is communication between cells.
73
What are glycoproteins
Carbohydrate chains attached to extrinsic proteins on the outer surface
74
The fluid-mosaic model
- fluid -> the phospholipid molecules can move relative to one another
- mosaic -> proteins are embedded in the surface of the membrane like a mosaic
75
Types of movement across the cell membrane
- diffusion
- facilitated diffusion
- active transport
- osmosis
76
What is diffusion
Net movement of molecule or ions from an area of high concentration to an area of low concentration until evenly distributed
-> passive process (no energy needed)
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What affects rate of diffusion
- conc gradient -> the greater the difference the faster
- area over which it takes place
- thickness of exchange material -> the thinner the faster
78
What is facilitated diffusion
Exactly like diffusion but protein and/or carrier proteins are involved
79
What proteins are involved in facilitated diffusion
Carrier proteins and protein channel
80
Structure of Protein channels
Water filled hydrophilic channels across the membrane
81
What do protein channels do
- allow specific water soluble ions to pass through
- the channels are selective -> only open in the presence of a specific ion which binds to them and causes them to change shape so it opens on 1 side and closes on the other
82
How do carrier proteins work
- when a specific molecule binds with the protein it causes it to change shape so that the molecule is released on the other side of the membrane
83
What is active transport
The movement of molecules of ions or out a cell from an area of lower concentration to an area of higher concentration using ATP and carrier proteins
84
How does active transport differ from passive forms of transport
- metabolic energy in form of ATP is needed
- substances are mixed against concentration gradient
- carrier proteins are used
- very selective process
85
Why does a graph of facilitated diffusion level off
Protein channels are saturated
86
What is osmosis
The movement of water from a region of high water potential to an area of lower water potential through a partially permeable membrane
87
What is water potential
The pressure created by water pressure
88
What is the water potential of pure water
Under standard conditions of temp and pressure it is 0
89
What does the addition of a solute to pure water cause
It will lower the water potential, so the water potential of a solution is always less than 0 (so a negative value)
90
What is hypotonic
The solution has a higher water potential than the inside of the cell so water moves in by osmosis
91
Hypotonic solution in animal cell
Animal cells swell up and will eventually burst as their cell membrane isn’t strong enough to withstand pressure (lysis)
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Hypotonic solution in a plant cell
They swell up but don’t burst because their cell wall protects them -> their vacuoles expand and they become **turgid** as the cell membrane pushes on the cell wall
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What is isotonic
No difference in water potential between the cell and surrounding solution so no net movement of water
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What is hypertonic
When the solution has lower water potential than the inside of the cell so water will move out of the cell by osmosis
95
Hypertonic solution in animal cell
Animal cells will shrivel as they lose water from their cytoplasm
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Hypertonic solution in plant cells
Plant cells are protected from shrinking but their vacuoles shrink and eventually their cell membranes pull away from the cell walls -> this is plasmolysis
97
Increasing the rate of movement across the ileum
The epithelial cells lining the ileum have microvilli which provide more SA for the insertion of carrier proteins
98
Why must active transport happen as well as diffusion in absorption
Because diffusion only works until the concentrations are equal meaning not all glucose and amino acids are being transported so active transport is used
99
What is the name for how amino acids and glucose are absorbed into the blood and why
Co-transport because the glucose or amino acids have been transported in along with sodium ions which have been actively transported out by the sodium-potassium pump
100
Where and how does the co-transport of glucose happen
In one type of protein-carrier molecule
1. Na+ are actively transported out of the epithelial cells into blood
2. This now leads to a lower concentration of Na+ in the cell
3. This causes Na+ to move into the epithelial cells from the ileum by facilitated diffusion -> this also brings in a glucose molecule (co-transport)
4. Glucose now moves down the concentration gradient from the epithelial cell to the blood by facilitated diffusion
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What is it that powers the movement of glucose and amino acids into cells and why
Not ATP but the sodium ion concentration gradient as the glucose molecules are moving against the concentration gradient and the sodium ions are moving down it easily
102
Densities of organelles
Nucleus
Chloroplast
Mitochondria
Lysosomes
Endoplasmic reticulum
Ribosomes
103
What do the most dense organelles form at the bottom of the centrifuge
Pellets
104
What stage of the cell cycle requires ATP
Anaphase
105
Mitotic index
( Number of cells in mitosis/ number of cells in view ) x 100
106
What are peripheral/extrinsic proteins
Proteins on the cell surface membrane only present on one side
-> provide support or involved in cell recognition
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What are integral/intrinsic proteins
Proteins that span across the cell surface membrane
-> incl. carrier proteins or channel proteins involved in the transport of molecules and ions across the membrane
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What are protein channels
Tubes that fill with water to enable to water soluble ions to diffuse
-> selective as channel only opens in the presence of certain ions
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What do carrier proteins do
Bind with larger molecules like glucose and amino acids and change shape to transport them to the other side of the membrane
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What kind of molecules require facilitated diffusion
Ions and polar substances
111
What is water potential
Pressure created by water molecules and is measured in kPa
112
Active transport process
1. Transport is through carrier proteins spanning the cell membrane
2. Molecule binds to a receptor complementary in shape on the protein
3. ATP binds to the carrier protein from the inside of the cell and it is hydrolysed into
ADP +Pi
4. This causes the carrier protein to change shape and release the molecule to the other side
5. The phosphate ion is then released and the protein returns to its original shape
113
Co-transport of glucose and sodium ions in the ileum
1. Sodium ions are actively transported out of the epithelial cell into the blood
2. This reduces the sodium ion concentration in the epithelial. cell.
3. Sodium ions can then
diffuse from the lumen down their concentration gradient into the epithelial cell
4. The protein the sodium ions diffuse through is a co-transported protein, so either glucose or amino acids also attach and are transported into the epithelial cell against their concentration gradient
5. Glucose then moves by facilitated diffusion from the epithelial cell to the blood
114
What does the sapsucker do
- prevent excess water loss
- prevent the host cells immune system getting in
115
Scanning electron microscope provide a..
3D image of the outer surface of a sample
116
Transmission electron microscopes provide a..
2D image of the samples internal structure
117
Similarities with TEM and SEM
- both use electrons
- both use vacuums/ can’t use live tissue
- both have higher magnification than optical microscopes
- both have higher resolution than optical microscopes
118
Differences with TEM and SEM
- electrons are transmitted through specimen in TEM whereas electrons are reflected off surface in SEM
OR
- TEM shows internal structure whilst SEM shows outer surface
- SEM produced 3D image whilst TEM can’t
- TEM gives higher resolution than SEN
- SEM can be used in thicker specimens than TEM
- TEM has higher max magnification than SEM
119
Glycolipid function
Acts as recognition sites for other cell
-> this allows cells to attach to each to form tissues
120
What are the 2 functions of a glycoprotein
Act as recognition sites for foreign cells and specific chemicals
121
Water as a metabolite
Used or formed in many chemical reactions in the body
122
Water as a solvent
Readily dissolved ions and polar molecules
123
Water and it’s high specific heat capacity
Means a lot of energy is needed to change it’s temperature and do acts as a buffer for changes in temperature
124
Water as having high latent heat of vaporisation
Meaning a lot of energy is needed to turn liquid water into water vapour so water can provide a cooling effect through evaporation
125
Compare the structure of a RBC with the structure of a plant cell
• Both have cytoplasm and cell membrane
• RBC has no nucleus, plant cell does
• RBC has no cell wall, plant cell does
• RBC does not contain chloroplasts or chlorophyll, plant cell does
• RBC has no (permanent) vacuole, plant cell does
• RBC contains haemoglobin, plant cell don't
126
Describe how to use a microscope to view cells
1. Clip slide onto stage and turn on light
2. Select lowest power objective lens
3.
a. Use coarse focusing dial to move stage close to lens
b. Turn coarse focusing dial to move stage away from lens until image comes into focus
4. Adjust fine focusing dial to get clear image
5. Swap to higher power objective lens, then refocus
127
How can sizes of cells be estimated using a microscope
1. Measure the diameter of field view
2. Divide this by number of cells that span the field of view
128
Why use a stain
To make subcellular structures visible
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Why is a thin layer of onion tissue used
To let light pass through
130
Why is the cover slip lowered at an angle
To avoid trapping bubbles
131
Why is it easier to view cells using the low power objective lens first
• biggest field of view
• easier to focus on
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A student collected a sample of cells by taking a saliva swab on the inside of their cheek.
Explain one safety measure that the student should take during this procedure.
1. Wear gloves/wash hands
-> because stain is an irritant
2. Disinfect work surfaces
-> to prevent spread of possible infection
133
How colour a student observe structures within a cell in grater detail
Use a higher power objective lens
-> or use an electron microscope
134
Fungal cells
Dont have chloroplasts
Cell wall is chitin not cellulose
135
Organ System
This is a group of organs working together to carry out a particular function
136
What do goblet cells do in ciliated epithelium
release mucus to trap pathogens, whilst the ciliated epithelial cells use cilia to sweep the mucus away
137
Smooth muscle tissue
found in walls of organs
138
Cardiac muscle tissue
Found in the heart
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Skeletal muscle tissue
found attached to bones
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Ciliated epithelium tissue
lines organs such as the trachea where it can sweep mucus away from the lungs.
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What cells make up ciliated epithelium tissue
ciliated epithelial cells and gobelt cells
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What is cartilage
type of connective tissue that acts as a cushion between bones
143
What is muscle tissue
Made up of muscle fibres
-> these fibres contract (shorten) and relax to move different parts of the body
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What is the capsule in prokaryotic cells made up of
Polysaccharides
145
What does the capsule do
Protect cells from attack by antibiotics or WBCs
146
What are capsids in viruses made up of
Protein
147
Converting units
cm -> mm = x10
mm -> hm = x1000
hm -> nm = x1000
148
Sample preparation - water sampling
1. Use a pipette to place a small drop of water onto the centre of the glass slide
2. Use a pair of forceps to place a thin section of the specimen onto the drop of water
-> the specimen should be thin enough to allow light to pass through
3. Add a few drops of stain to the specimen.
-> this increases contrast and allows cell components to become visible
4. Slowly add a cover slip onto the specimen
149
Using a light microscope
1. Clip the prepared microscope slide onto the stage
2. Select the objective lens with the lowest power
3. Use the coarse focus to bring the stage just below the objective lens
4. Look down the eyepiece and use the coarse focus to move the stage downwards until the image is roughly in focus
5. Use the fine focus to make the image clearer
6. If a higher magnification is needed, swap to a more powerful objective lens and refocus
150
Biological drawings should:
- Include a title
- State the magnification or scale
- Be drawn with a sharp pencil
- Include smooth, continuous lines
- Include labels
- Include accurate sizes of observable structures
151
Biological drawings should not:
- Include shading or colouring
- Include arrow heads for labels
- Involve lines overlapping each other
152
What happens during interphase
1. Cell growth - This includes an increase in cytoplasm.
2. Synthesis of proteins - These proteins are used to replicate organelles.
3. Replicating DNA - This results in double the genetic material.
153
What do chromosomes consist of
DNA coiled around proteins called histones
154
Binary Fission
1. Cell growth - The cell increases in size to prepare for division.
2. DNA replication - The circular chromosome is replicated once, and plasmids may be replicated multiple times.
3. Movement of DNA - Each replicated circular chromosome moves to opposite poles of the cell, and plasmids are distributed randomly between the two poles.
4. Cell wall growth - The cell-surface membrane starts to divide and new cell walls form between the two DNA molecules.
5. Cytoplasm division - The cytoplasm of the original cell is divided into two identical daughter cells.
155
What do carrier proteins transport across the membrane vs channel proteins
Carrier Proteins: large molecules
Channel Proteins: ions
156
How do channel proteins work
They form pores in the cell membrane which ions can travel through
156
How carrier proteins work
1. A large molecule attaches to a carrier protein
2. This causes the carrier protein to change shape
3. The carrier protein releases the molecule on the opposite side of the membrane
157
What is water potential
The pressure exerted by water molecules on the membrane (or container) surrounding a solution.
-> It is measured in kiloPascals (kPa)
158
What methods of transport use carrier proteins
Facilitated diffusion and active transport
159
How does a carrier protein help in active transport
1. The molecule or ion binds to the carrier protein
2. ATP binds to the carrier protein.
Hydrolysis of ATP to ADP and phosphate (Pi) causes the carrier protein to change shape
--> this releases the molecule or ion on the opposite side of the membrane
3. The phosphate (Pi) is released from the carrier protein, causing the carrier protein to return to its original shape, ready to be used again
160
The 3 different proteins used in co-transport of glucose
1. Sodium-potassium pumps
-> these actively transport sodium (Na+) and potassium (K+) ions.
2. Sodium-glucose co-transporter proteins
-> these use facilitated diffusion to transport Na+ ions and glucose molecules
3. Glucose protein channels
-> these use facilitated diffusion to transport glucose molecules.
161
Why do glucose molecules move by co-transport rather than active trnasport
because they are moved against their conc gradient due to the Na+ conc gradient, rather than by using ATP
162
Co-transport of sodium and glucose
1. Na+ is actively transported out of epithelial cells into the blood by the sodium-potassium pump
-> this creates a concentration gradient as there is now a higher concentration of Na+ in the lumen than in the epithelial cells
2. Na+ diffuses from a high concentration in the lumen to a low concentration in the epithelial cells
-> it is transported via sodium-glucose co-transporter proteins, which also carry glucose molecules
-> this causes the concentration of glucose inside the epithelial cells to increase
3. There is now a higher glucose concentration in the epithelial cells than in the blood
-> so, glucose diffuses out of epithelial cells and into the blood via facilitated diffusion
163
What is ATP used for in costranport of glucose and soidum ions
to maintain the conc gradient of sodium ions between the lumen and the epithelial cells of the ileum
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