Section 3 - organisms Exchange substances with their environment Flashcards
Define digestion
The hydrolysis of large insoluble molecules into smaller molecules taht can be absorbed across cell membranes.
Which enzymes are involved in acrogydrate digestion and where are they found?
- salaivary amylase in mouth. pancreatic amylase in pancreas.
- Maltase, sucrase, lactase in membrane of small intestine as memebrane bound enzymes.
What are the substrates and products of the carbohydrate digestive enzymes?
Amylase -> starch into smaller polysaccarides such as maltose.
Maltase -> maltose into 2 x Alpha glucose.
Sucrase -> scucrose into glucose and fructose.
Lactase -> lactose into glucose and galactose.
Where are lipids digested / hydrolysed?
The small intestine (ileum)
What needs to happen before lipids can be digested/ hydrolysed?
They must be emulsified by bile salts produced by the liver. this breaks down large fat molecules into smaller soluble droplets surrounded by bile salts to form micelles. this increases surface area. for lipase to work on.
Which enzymes are involved in protein digestion? What are their roles?
-Endopeptidases = breaks bonds between amino acids in the middle of a polypepetide.
-Exopeptidases = break bonds between amino acids at the end of a polypepetide
-Dipeptidases (membrane bound) break dipeptides into amino acids.
What is co-transport?
- The coupled movement of substances across a cell membrane via a carrier protein Despite a negative concentration gradient
- This involves a combanation of facilitated diffusion and active transport.
Which molecules require co -transport in the ileum and how does this happen?
- sodium and glucose and amino acids.
- The active transport of sodium ions from the epithelial cell into the blood via the sodium potassium pumplowers the concentration inside the cell and generates a sodium ion concentration gradient between the ileum and the epithelial cell
- sodium ions move into the cell from the ileum via faccilated diffusion carrying glucose molecules with them via a cotransport protein
- the glucose concentration inside the epithelial cell increases and glucose molecules eneter the blood via facillitated diffusion
Why do fatty acids and monoglycerides not require co transport?
the molecules are non-polar, meaning they can easily diffusr across the membrane of the epithelial cells
how do you calculate the surface are to volume ratio?
surface area: the area of all the faces added together
volume : l x w x h
larger organisms have a smaller surface are to volume ratio.
what three factors affect the rate of diffusion?
- high surface area
- short diffusion distance
- high concentration gradient.
how do insects perform gas exchange?
- air enters through holes called spiracles
- oxygen diffuses down the concentration gradient along the trachea
- oxygen diffuses into the cells
- ventilation helps to maintain a high concentration gradient
how does the structure of an insect help it to reduce water loss?
- body is covered by a waxy cuticle this reduces evaporation
- spiracles can be closed to reduce water loss
how do fish perform gas exchange?
- filaments and lamellae have a big surface area
- this increases the efficiency of diffusion
- thin epithelium have a short diffusion distance
what is counter currant flow?
- blood and water move in opposite directions
this maintains a high concentration gradient - a water is always next to blood with a lower concentration of oxygen
- the circulation of blood replaces blood that is saturated with oxygen
- ventilation of water.
what is the structure of the lungs?
- traches branches into the bronchi which branches out into the bronchioles which have alveoli on the end
- externally we have the lung, the ribs with external and internal intercostal muscles and the diaphragm.
What happens in the pulmonary circulatory system?
1 deoxygenated blood is pumped out of the heart via the pulmonary arteries to the lungs
2. deoxygenated blood is returned to the heart via the pulmonary vein from the lungs.
what are the adaptations of the lungs that contribute to efficient gas exchange?
- alveoli contribute to a large surface area with many capillaries for fast diffusion
- alveoli and capillaries ae one cell thick, these contribute to a short diffusion pathway for faster diffusion
what is the structure of the heart?
what happens in the systemic circulatory system?
- oxygenated blood is pumped out of the heart via the aorta to most body tissues
- other blood vessels branch from the aorta to deliver blood
- veins collect deoxygenated blood
- deoxygenated blood is returned to the heart via the vena cava
what occurs in gas exchange?
- carbon dioxide rich air moves out of the alveoli while oxygenated air moves in. (ventilation)
- the oxygen diffuses into the blood stream through simple diffusion
what is a double system?
- blood passes through the heart twice per unit.
how does the heart function?
Deoxygenated blood enters the right atrium from the vena cava.
Blood moves into right ventricle.
Blood is pumped into the pulmonary artery.
The pulmonary artery carries deoxygenated blood to the lungs.
The blood becomes oxygenated in the lungs.
Oxygenated blood leaves the lung via the pulmonary vein.
Blood enters the left atrium.
Blood moves into the left ventricle.
Blood is pumped into the aorta, which carries oxygenated blood around the body.
what is the purpose of the pulmonary artery??
to carry deoxygenated blood to the lungs
what is the purpose of the aorta?
- to carry oxygenated blood the body
what is the purpose of the atrio ventricular valves?
- unidirectional flow of blood (prevents back flow)
-open when the pressure is higher in thee atrium then in the ventricle
what is the purpose of the semilunar valves?
- they open when the pressure is bigger in the ventricles then in the blood vessels.
- prevent back flow.
How does haemoglobin transport oxygen?
- Red blood cells contain haemoglobin, which has 4 haem groups,
- In the capillaries in the lungs, oxygen binds to iron in haem groups, forming oxy haemoglobin
- Each haemoglobin molecule can carry 4 oxygen molecules, one per h group
- Oxyhaemoglobin can be transported via blood to respiring body tissues
- At body cells, oxygen dissociates from haemoglobin
What factors affect haemoglobin concentration in the blood?
- oxygen concentration or partial pressure of oxygen p02
How does p02 affect haemoglobin saturation?
- Higher p02 means that haemoglobin has a high affinity for oxygen and binds with it
- Lower p02 means haemoglobin has a low affinity for oxygen and releases it.
How does haemoglobin saturation change depending on how much oxygen is bound to it?
- when haemoglobin binds with one oxygen, it changes shape so it becomes easier to bind another oxygen
- when haemoglobin is mainly saturated with oxygen, it is harder for more oxygen to bind.
what is the difference between fetal haemoglobin and adult haemoglobin?
- the fetus needs to obtain oxygen from the mother’s blood.
- the fetal haemoglobin therefore has a higher oxygen affinity than the adult haemoglobin found in the mother’s blood
- this allows the oxygen to dissociate from the mother’s haemoglobin and bind to haemoglobin in the fetal blood.
- this ensures that the fetus gets enough oxygen to survive while it develops.
how does the pressure of C02 affect haemoglobin saturation?
- higher C02 at respiring tissues causes haemoglobin to release oxygen.
- Bohr effect decreased affinity for oxygen in haemoglobin when C02 is present.
- This means the oxygen saturation of haemoglobin is lower for a given pC02 when PC02 is higher.
why do multicellular organisms need transport systems?
- too big for simple diffusion as the diffusion distance would be too large.
- have a higher metabolic rate
- large number of active cells
what is a closed system?
- blood is contained in blood vessels
Why do the ventricles have thicker walls than the atria?
- the atria only need enough pressure to pump blood a distance into the ventricles
- the ventricles need a lot of pressure to pump blood a long distance
why is the left ventricle wall thicker than the right ventricle wall?
- the right ventricle only pumps to the lungs but the left ventricle pumps to the body.
what are the stages of the cardiac cycle?
- the cardiac cycle is the sequence of contraction and relaxation of the cardiac muscle in the walls of the heart.
atrial systole, ventricular systole and diastole.
what happens in atrial systole?
- the ventricles relax and the atria contract
- this increases the atrial pressure
- the atrioventricular valves open
- blood flows into the ventricles
what happens in ventricular systole?
- the ventricles contract and the atria relax.
- the ventricular pressure increases
- The semi-lunar valves open and the atrioventricular valves close
- blood flows into the arteries
what happens in diastole?
- the ventricles and atria relax/
- the semi-lunar valves close
- blood flows passively into the atria
what is cardiac output?
- the volume of blood pumped by one ventricle of the heart in one minute.
how do you calculate the cardiac output?
- measure the heart rate
- measure the stroke volume (volume of blood pumped by the left ventricle during systole
- calc the cardiac output. - heart rate x stroke volume
How are arteries adapted for blood flow?
- collagen - provides strength to prevent the vessel from bruising and maintains shape
- elastic fibres contain elastin that lets them stretch and recoil to minimise changes in pressure
- thick smooth muscle layer - contracts / relaxes to control blood flow.
what do arteries do?
carry blood at high pressure away from the heart.
what are arterioles?
Arterioles are smaller than arteries but with a comparatively larger lumen. Their walls have more smooth muscle and less elastin as they do not need to withstand such high pressures.
What are vasoconstriction and vasodilation
- Vasoconstriction - Smooth muscle contracts, constricting the blood vessels and decreasing blood flow.
- Vasodilation - Smooth muscle relaxes, dilating the blood vessels and increasing blood flow.
What are capillaries?
- capillaries form extensive networks between arterioles and venules, providing an area between blood and tissues where exchange of substances like gases and nutrients can occur.
What are the adaptations of capillaries?
- lumen is very narrow - allows for blood cells to be close to body cells
- walls are thin - substances can be exchanged across a short distance by diffusion
- highly branched.
- provides a large surface area for diffusion
What are veins?
- vessels that carry blood to the heart at low pressures
What are the adaptations of veins?
- collagen provides strength to prevent the vessel from bursting and maintaining vessel shape.
- little smooth muscle and elastic fibre not much is needed due to low-pressure
- valves to prevent the backflow of blood.
what are venules?
-Venules are smaller than veins. They have very thin walls and very little smooth muscle. Both venules and veins have valves.
- what does blood consist of?
- plasma
- red blood cells
- white blood cells
- platelets (clotting)
What are the functions of blood?
- transports oxygen and carbon dioxide
- transports nutrients from digestion
- transports waste for excretion
- transports hormone
- transports food from storage
- transports clotting factors
what is tissue fluid?
- tissue fluid fills spaces between cells. it is the site of diffusion between blood and body cells.
what is the composition of tissue fluid
- has the same composition as plasma but
- no red blood cells
- fewer proteins
- fewer white blood cells.
how is tissue fluid formed? at the arteriole end of capillaries?
- a high hydrostatic pressure, exerted by the force of the heart pumping, forces fluid out of capillaries
- this forms tissue fluid surrounding body cell
How is tissue fluid formed at the venule end of capillaries?
- the hydrostatic pressure is lower
- proteins in the blood exert a high oncotic pressure (osmotic pressure) in capillaries
- the water potential is lower in capillaries than in tissue fluid due to fluid loss
- some tissue fluid moves back into the capillaries by osmosis.
What is lymph?
- Lymph is the fluid that flows around the lymphatic system via lymph vessels.
What is the composition of lymph?
- same as tissue fluid but
- less oxygen and nutrients
- more fatty acids
- more white blood cells.
How is lymph formed and transported?
- Some tissue fluid doesn’t re-enter capillaries from tissue fluid.
- This fluid instead drains into lymph vessels (lymph capillaries) forming lymph.
- Lymph is transported through lymph vessels by muscle contractions.
- Lymph is passed through lymph nodes to filter pathogens.
- The lymph is eventually returned to the blood.
Why do organisms need transport systems?
- because they are multicellular with a low surface area to volume ratio
- diffusion is too slow to meet their metabolic needs
- substances must be moved long distances
What is xylem tissue?
- Xylem tissue transports water and mineral ions around plants, it also provides structural support
- made up of xylem vessels
What are the adaptations of xylem tissue?
- elongated hollow tubes without end walls
- they lack organelles
- their walls are thicker with lignin for support
- they have non-lignified pits that allow for the movement of water and other ions in and out of vessels
What is phloem tissue?
- Phloem tissue transports sugars and amino acids around plants, it is mostly made up of sieve tube elements and companion cells
What are the adaptations of sieve tube elements?
- they are connected end-to-end to form sieve tubes
- they have sieve plates with pores at their ends to allow the flow of sugars and amino acids
- they lack nuclei and most organelles
- they only have a thin layer of cytoplasm
What are the adaptations of companion cells?
- they are connected to sieve tube elements through pores (plamodesmata)
- The cytoplasm contains a large nucleus and many mitochondria that release energy for the active transport of substances through the sieve tube elements . and many ribosomes for protein synthesis
How does water move through a plant?
- water enters a plant’s root hair cells via osmosis
- it moves through the cell cytoplasm or cell walls towards the xylem
- The xylem transports water from the roots up to the leaves
- Water is used for photosynthesis
- Some water evaporates from leaf cells by transpiration and diffuses out of the plant
What is cohesion-tension theory?
- explains how water moves up towards the xylem against gravity
How does the cohesion-tension theory work?
- cohesion - hydrogen bonding causes water molecules to stick together and move as one continuous column
- adhesion - hydrogen bonding between polar water molecules and non-polar cellulose pulls water upwards through the xylem
- transpiration - evaporation of water at the leaves creates the transpiration pull, and this tension is transmitted down the whole water column due to cohesion
What is transpiration?
- The evaporation of water from aerial parts of plants. especially the leaves
How does transpiration work?
- water evaporates from the moist surfaces of mesophyll cells
- stomata open so they can absorb carbon dioxide for photosynthesis
- This provides a pathway for water vapour loss through open stomata
- Water vapour moves down a water potential gradient from spaces in the leaf into the atmosphere.
How does light intensity affect the transpiration rate?
- At high light intensities, the stomata open for maximum C02 absorption for photosynthesis, increasing the transpiration rate.
How does temperature affect the transpiration rate?
- at high temperatures, evaporation of water molecules is faster due to higher kinetic energy, increasing the transpiration rate
How does humidity affect the transpiration rate?
- low humidity increases the water vapour gradient between the leaf and atmosphere, increasing the transpiration rate
How does wind speed affect the transpiration rate?
- high wind speeds increase the water vapour gradient between the leaf and atmosphere, increasing the transpiration rate.
how do you use a potometer?
- Cut the shoot underwater at a slant to increase the surface area for water uptake
- Assemble the photometer with the shoot submerged in water
- Keep the capillary tube end of the photometer submerged throughout the experiment
- Check that the apparatus is air-tight
- Dry the leaves and give the shoot time to acclimate
- Shut the tap from an air bubble and record its position
- Measure the distance the air bubble moves at the time taken
- Change one variable at a time and keep everything else constant.
How can you calculate the rate of transpiration using a potometer?
- Calculate the cross-sectional area of the capillary tube (pir^)
- Calculate the volume of water uptake by multiplying the cross-sectional area by the distance the air bubble traveled
- Rate of transpiration volume of water uptake/time taken
What is translocation?
- the mass flow of solutes, sucrose and amino acids, from one part of a plant to another part of the plant.
What are the features of translocation?
- requires energy
- transports substances from sources to sinks
- the substances are transported through the phloem
- water provides the medium in which these substances dissolve for transport
- maintains a conc gradient using enzymes
What is mass flow hypothesis?
- at the source solutes are activley loaded into sieve tube elements from companion cells
- this decreases the water potential in sieve tube elements
- water enters the sieve tube elements from the xylem and companion cells by osmosis
- This increases hydrostatic pressure at the sink, and solutes are actively removed from sieve tube elements
- this increases the water potential in sieve tube elements at the sink
- water leaves the phloem by osmosis decreasinf the hydrostatic pressure at the sink
- This creates a pressure gradient , pushing solutes from the source to areas of lower pressure at the sink
What is evidence for the mass flow hypothesis?
- the stem bulges with fluid containing more sugar above sections where a ring of bark should be removed
- This shows that the removal of phloem prevents the downward flow of sugars - Radioactive isotopes of carbon in the form of CO2 that are supplied to a leaf is incorporated into organic substances and can be traced around the plant.
This shows that organic substances move from source to sink - Sap fed on by aphids flows out of the stem more quickly at the top of the stem.
This shows that there is a pressure gradient in the phloem. - Translocation stops when inhibitors that prevent ATP synthesis are added to the phloem.
This shows that some aspect of translocation requires energy.
What is some evidence against the mass flow hypothesis?
- sugars do not just move to sinks with the highest water potential
- The pressure gradient wouldn’t be high enough for a sufficient rate of low through sieve plates, especially through large trees.
