Organisms exchange substances with their environment Flashcards
What are the three disaccharides in the spec. to do with digestion
• Maltose
• Sucrose
• Lactose
What enzymes hydrolyse disaccharides
Disaccharidases
What disaccharidase hydrolyses maltose
Maltase
What disaccharidase hydrolyses sucrose
Sucrase
What disaccharidase hydrolyses lactose
Lactase
What are the products of the hydrolysis of maltose
Glucose + Glucose
What are the products of the hydrolysis of sucrose
Glucose + Fructose
What are the products of the hydrolysis of lactose
Glucose + Galactose
Why’s there no carbohydrate digestion in the stomach (2)
- Too acidic for salivary amylase
- Stomach enzymes only digest proteins
What are membrane bound disaccharidases
Enzymes attached to the cell surface membrane of epithelial cells lining the ileum
How is fructose absorbed
Via facilitated diffusion through a transport protein
How are glucose and galactose absorbed (the two G’s)
By active transport with Na+ ions via a co-transporter protein
What is digestion of lipids
Hydrolysis of ester bonds
What are triglycerides broken down into
A monoglyceride and two fatty acids
How are fatty acids absorbed into the blood
By simple diffusion
What enzyme hydrolyses lipids
Lipase
Where are lipase enzymes produced
The pancreas where they’re secreted into the small intestine in pancreatic juice
Where are bile salts produced
The liver
What do bile salts do
Lower surface tension between lipids and water so large drops of lipid split into smaller ones (Emulsification)
What’s emulsification
Bile salts lower surface tension between lipids and water so large drops of lipid split into smaller ones
What does emulsification do
Increases surface area for lipase enzymes to act on
How are micelles formed
The products of lipid digestion (monoglyceride + fatty acids) stick to bile salts to form micelles
What’s a micelle
the products of lipase digestion that remain in association with the bile salts to form structures
What do micelles do
• Help move monoglycerides and fatty acids to the epithelial cells
• constantly break up and reform so they can release their monoglycerides and fatty acid, allowing them to be absorbed
What is protein digestion
Hydrolysis of peptide bonds
What enzyme breaks down protein
Protease
What are the three types of protease
- Endopeptidase
- Exopeptidase
- Membrane bound dipeptidase
What do endopeptidases do
Hydrolyse peptide bonds within a protein
What do exopeptidases do
Hydrolyse bonds one bond from the end of a protein
What do membrane bound dipeptidases do
Hydrolyse bonds in dipeptides while attached to the cell surface membrane for epithelial cells in the ileum
What’s the product of protein digestion
Amino acids
How are amino acids absorbed
(Similarly to glucose and galactose) By co-transport through an Na+ co-transporter protein to the lumen
Why must heat be exchanged by organisms with their environment
To maintain a constant temperature
What happens if waste products build up
Cells die
Gaseous exchange definition
Diffusion of oxygen from the air in the alveoli into the blood and of carbon dioxide from the blood into the air in the alveoli
Adhesion definition
• Attraction of molecules of one kind for molecules of a different kind
• It can be quite strong for water, especially with other molecules bearing positive or negative charges
Cohesion definition
• Attraction between molecules of the same type
• How water molecules form hydrogen bonds between one another and hence tend to stick together
What’s the cohesion-tension theory
The main factor that’s responsible for the movement of water up the xylem, from the roots to the leaves.
Transpiration pull puts the xylem under tension (there is negative pressure within the xylem) and because of the cohesive nature of water (due to hydrogen bonds between water molecules) there is a continuous stream of water being pulled across the mesophyll cells and up the xylem
What’s a companion cell
Since the sieve tube element lacks organelles, the companion cell controls the movement of solutes and provides ATP for active transport in the sieve tube element.
What connect the sieve tube element and the companion cell
Strands of cytoplasm called plasmodesmata
Diffusion definition
The movement of molecules or ions from a region where they’re in high concentration to one where their concentration is lower
What’s a guard cell
One of a pair of cells that surround a stoma in plant leaves and controls it’s opening and closing
What’s a hydrogen bond
Chemical bond formed between the positive charge of a hydrogen atom and the negative charge on another atom of an adjacent molecule
Hydrolysis definition
The breaking down of larger molecules into smaller ones by the addition of water molecules
What’s an ion
An atom or group of atoms that has lost or gained one or more electrons
What’s an ion channel
A passage across a cell surface membrane made up of a protein that spans the membrane and opens and closes to allow ions to pass in and out of the cell
Isotonic definition
Solutions that possess the same concentration of solutes and therefore have the same water potential
What’s the mass-flow theory
• The bulk movement of a substance through a given channel or area in a specified time.
• Sucrose is transferred into sieve elements from photosynthesising tissue so there can be mass flow of sucrose solution down a hydrostatic gradient in sieve tubes
• caused by active transport (of sucrose into sieve tubes at the source and out of sieve tubes at the sink)
• and osmosis (movement of water into sieve tubes near sources and out of sieve tubes near sinks)
What’s mesophyll
Tissue found between the two layers of epidermis in plant leaves comprising an upper layer of palisade cells and a lower layer of spongey cells
Metabolism definition
All the chemical processes that take place in living organisms
What are Microvilli
Tiny, finger-like projections from the cell surface membrane of some animals
What are middle lamella
Layer made up of pectins and other substances found between the walls of adjacent plant cells
What’s mitosis
The type of nuclear division in which the daughter cells have the same number of chromosomes as the parent cell
What’s a monomer
One of the many small molecules that combine to form a polymer
Osmosis definition
The movement of water from a region of high water potential to a region of lower water potential through a partially permeable membrane
What are palisade cells
Long, narrow cells packed with chloroplasts that are found in the upper region of a leaf and which carry out photosynthesis
What’s the phloem
Plant tissue that transports the products of photosynthesis from leaves to the rest of the plant
What’s a potometer
A piece of apparatus which measures the rate of water loss in a plant
What would you use to measure the rate of water loss in a plant
A potometer
What’s a protoplast
The living portion of a plant cell (i.e. the nucleus and cytoplasm along with the organelles it contains)
What’s ringing
• An experiment when a section of outer layers (protective layer and phloem) is removed around the complete circumference of a woody stem while it’s still attached to the rest of the plant.
• This results in the region of the stem immediately above the missing ring of tissue swelling because the sugars of the phloem accumulate above the ring and it leads to tissues dying below the ring because of the interruption of flow of sugars to this region.
What does ringing show
That the phloem is responsible for translocating sugars
What’s a sieve tube element
Living, tubular cells that are connected end to end. The cell walls have perforations in them to make sieve plates.
The cytoplasm’s present but in small amounts and in the layer next to the cell wall.
It lacks a nucleus and most organelles so there’s more space for solutes to move.
The cell walls are made of cellulose so solutes can move laterally as well as vertically.
Next to each sieve tube is a companion cell
What’s a stoma (stomata)
A pore, mostly in the lower epidermis of a leaf through which gasses diffuse in and out of the leaf
What’s a tracer
• Radioactive isotopes can be used to trace the movement of substances in plants.
• ^14CO2 is used so plants incorporate this isotope into the sugars produced during photosynthesis.
• These radioactive sugars can then be traced as they move within the plant using autoradiography
How can radioactive sugars be traced moving through a plant
Autoradiography
What radioactive isotope is used to trace the movement of substances in plants
^14 CO2
What do tracers show
Sugars are found where phloem tissue is in the stem
What’s translocation
The process by which organic molecules and some mineral ions are transported from one part of a plant to another
What’s transpiration
The main force that pulls water through the xylem vessels in the stem of a plant is the evaporation of water from leaves through stomata
What’s transpiration pull
How a column of water is pulled up the xylem as a result of transpiration
What’s water potential
The pressure created by water molecules.
The measure of the extent to which a solution gives out water
What are xylem vessels
Dead, hollow, elongated tubes with lignified side walls and no end walls, that transport water in most plants
Outline the mass flow hypothesis
- Companion cells actively transport hydrogen ions (H+) into the source cell
- This creates a concentration gradient of hydrogen ions between the source and companion cell
- H+ wants to diffuse back due to the new concentration gradient, sucrose is co-transported into the sieve tube with H+ through special transport proteins that require a sucrose molecule by companion cells
- Water potential in the sieve tubes’ lowered do water moves from the xylem into the sieve tube by osmosis
- Increased hydrostatic pressure
- Mass flow of substances (sucrose) to respiring cells in the sink
- Facilitated diffusion of sucrose from the phloem into the sink cells
- Water potential at the phloem increases, so water moves by osmosis back into the xylem
What evidence supports the fact that saps under positive pressure in the phloem within the mass flow hypothesis
When sieve tubes are cut, sap’s released
What does sap being released when sieve tubes are cut suggest
saps under positive pressure in the phloem within the mass flow hypothesis
What evidence supports the fact there’s a pressure gradient in the phloem within the mass flow hypothesis
• Aphids tap into the phloem to consume sap- the high pressure forces it through their digestive system resulting in the excretion of honeydew.
• Honeydew tends to flow faster out of aphids higher up the plant near leaves than lower down the stem.
What evidence supports the presence of sources and sinks within the mass flow hypothesis
Sucrose concentrations higher in leaves than roots
What does the fact sucrose concentrations higher in leaves than roots support in terms of the mass flow hypothesis
The presence of sources and sinks
4 pieces of evidence supporting the mass flow theory
- Increases in sucrose in leaves are followed by increases in sucrose in the phloem
- Downward flow in the phloem occurs in daylight when photosynthesis is occurring but not at night; due to greater respiration at night and lack of photosynthesis that would mean there would no longer be a pressure gradient
- Preventing ATP production stops translocation but not water movement. A lack of ATP for active transport in companion cells would kill them which would prevent mass flow
- Ringing
2 pieces of evidence against the mass flow hypothesis
- Sugar travels to many different sinks and doesn’t travel first or faster to the one with the highest water potential which it should according to the mass flow hypothesis
- The end plates of the sieve tubes would create a barrier to mass flow, or slow it down, so why are they present?
