Organisms exchange substances with their environment Flashcards
What is the role of the xylem tissue
Transports water and mineral ions in solution. These substances move up the plant from the roots to the leaves.
What is the role of the phloem tissue
Transports organic substances like sugars both up and down the plant
What is the structure of xylem vessels
Long, tube-like structures formed from dead cells joined end to end . No end walls, making an uninterrupted tube that allows. water to pass. up through the middle
How does water move up a plant against the force of gravity
-Water evaporates from the leaves at the top of the xylem (transpiration)
-Creates tension, which pulls more water into the. leaf
-Water is cohesive, so when some molecules are pulled others follow
-Column of water in the xylem moves upwards
-Water enters the stem through the roots
What is transpiration
The evaporation of water from a plant’s surface.
Water evaporates from the moist cell walls and accumulates in the spaces between cells in the leaf. When the stomata open, it moves out of the leaf down the concentration gradient.
What are the factors that affect transportation rate
-Light: The more light the faster the transpiration rate, because the stomata opens when it gets light to let in carbon dioxide for photosynthesis
-Temperature: The higher the temperature the faster the transpiration rate. Warmer water molecules have more energy so they evaporate faster. This increases the concentration gradient between the inside and outside of the cell.
-Humidity: The lower the humidity, the faster the transpiration rate. If the air around the plant is dry, the concentration gradient between the leaf and air increases.
-Wind: The windier it is, the faster the transpiration rate. Lots of air movement blows away water molecules.
What is the role of sieve tube and companion cells
Sieve tube elements are living cells that form the tube for transporting solutes. They have no nucleus and few organelles, so they have companion cells that carry out living functions for sieve cells
What is translocation
The movement of solutes (assimilates) to where they are needed in a plant. It requires energy and occurs in the phloem. Enzymes maintain concentration gradient from the source to the sink by changing solutes at the sink, to ensure the conc is lower at the sink.
Mass Flow Hypothesis
-Active transport is used to load the solute from companion cells into the sieve tubes of the phloem at the source.
-Lowers the water potential inside sieve tubes, so water enters the tubes via osmosis from the xylem and companion cells, creating a high pressure inside the sieve tubes at the source of the phloem.
-At the sink end, solutes are removed from the phloem to be used up, increasing water potential inside the sieve tubes, so water also leaves tubes by osmosis, lowering pressure in the sieve tubes.
-There’s a pressure gradient from the source the. the sink, which pushes solutes along sieve tubes. towards the sink.
What is a potometer
Apparatus used to measure transpiration rates by measuring water uptake
How to use a potometer
-Cut shoot (slanted to increase SA for water uptake) underwater to prevent air entering xylem.
-Assemble potometer with capillary tube end submerged in a beaker of water
-Insert shoot underwater
-Ensure apparatus is watertight and airtight
-Dry leaves and allow time for shoot to acclimatise, shut the tap
-Remove the end of the capillary tube from the water beaker until an air bubble forms, then put the tube back in water
-Record the start position of the air bubble
-Start a stopwatch and record the distance moved. by the bubble per unit time.
-Only change one variable at a time.
Evidence For Mass Flow
-If a ring of bark, including phloem and not xylem, is removed from a woody stem, a bulge forms above the ring. The fluid from bulge has a higher concentration sugars than fluid below the ring, evidence of downward flow of sugars
-Radioactive tracer can track the movement of organic substances in a plant.
-Pressure in phloem can be investigated with aphids. The sap flows out quicker nearer the leaves than further down the stem- evidence of pressure gradient.
-If a metabolic inhibitor (stops ATP production) is put in the phloem, translocation stops- evidence that active transport is involved
What does an aphid do
Pierces the phloem, then their bodies are removed leaving the mouthparts behind, allowing sap to flow out
Use this information and your knowledge of surface area to volume ratios to suggest an explanation for the position of mitochondria in large U. marinum cells.
Larger cells have a smaller surface area to volume ratio. Takes longer for oxygen to diffuse
Explain the advantage for larger animals of having a specialised system that facilitates oxygen uptake.
Larger animals have a smaller surface area to volume ratio, so a specialised system will help overcome long diffusion pathway
Mammals such as a mouse and a horse are able to maintain a constant body temperature.
Use your knowledge of surface area to volume ratio to explain the higher metabolic rate of a mouse compared to a horse.
Mice are smaller organisms and therefore have a larger surface area to volume ratio. This means that mice have a shorter diffusion pathway and heat can be lost more easily. Mice must have a high metabolic rate as a faster rate of respiration releases heat
The scientist used units of μmol g–1 h–1 for the rate of oxygen uptake.
Suggest why he used μmol in these units.
Measures small uptake
The scientist decided to use the ratio of surface area to mass, rather than the ratio of surface area to volume. He made this decision for practical reasons.
Suggest one practical advantage of measuring the masses of frog eggs, tadpoles and adults, compared with measuring their volumes.
Less error in measuring mass, easier to find mass because of irregular shapes
Explain why oxygen uptake is a measure of metabolic rate in organisms.
Oxygen is used in respiration which requires ATP
Explain how the counter-current principle allows efficient oxygen uptake in the fish gas exchange system.
Blood and water flow in opposite directions, blood always passes water with a higher oxygen concentration, there’s a diffusion gradient maintained along the length of lamella
The damselfly larva is a carnivore that actively hunts prey. It has gills to obtain oxygen from water.
Some other species of insect have larvae that are a similar size and shape to damselfly larvae and also live in water. These larvae do not actively hunt prey and do not have gills.
Explain how the presence of gills adapts the damselfly to its way of life.
Damselfly has a higher metabolic rate so uses more oxygen per unit mass
Explain two ways in which the structure of fish gills is adapted for efficient
gas exchange.
Many lamellae so large surface area, thin surface so short diffusion pathway
Explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange
Tracheoles have thin walls so short diffusion distance to cell.
They are highly branched so short diffusion distance to cells.
Trachea provides tubes full of air so fast diffusion into insect tissues.
Fluid at the end of the tracheoles that moves out into tissues during exercise so larger surface area for gas exchange.
Gas exchange insects
Air moves through spiracles on the surface, air moves through the trachea, gas exchange at tracheoles directly to/from cells.
Rhythmic. abdominal movements increase the efficiency of gas exchange by increasing oxygen entering → maintains greater conc gradient for diffusion.
Insects; adaptations
-Thick waxy cuticle → increased diffusion distance → less evaporation
-Spiracles can open and close → open to allow Oxygen in, close when water loss is too much
Structure of gills
Each gill is made of lots of thin plates (vertical) called gill filaments which provide large surface area. Gill filaments covered in lamellae (horizontal). Thin. epithelium short diff. distance between water and blood. Vast network capillaries on lamellae, removes oxygen. to maintain a concentration gradient.
Gas exchange in plants
CO₂ and O₂. diffuse through stomata, which is opened by guard cells. CO₂ and O₂ diffuse into mesophyll layer into air spaces down conc gradient.
Plants exchange; adaptations
-Lots of stomata that are close together →large surface area for gas exchange → gases don’t have to pass through cellist reach mesophyll.
-Interconnecting air space in mesophyll layers → gases come into contact with mesophyll cells
-Mesophyll cells have a large surface area
Xerophytic plants; adaptations
-Thick waxy cuticle →increased diffusion distance so less evaporation
-Stomata in pits, rolled leaves & hairs →trap water vapour →water potential gradient decreases → less evaporation
-Spindles → reduces surface area to volume ratio
Describe and explain the mechanism that causes lungs to fill with air.
Diaphragm muscle contracts and external intercostal muscles contract. Volume increases and pressure decreases. Air moves down a pressure gradient
Describe the gross structure of the human gas exchange system and how we breathe in and out.
Air enters the trachea, which split into two bronchi- one bronchus leading to each lung. Each bronchus branches off into smaller tubes ‘bronchioles’, which end in air sacs called alveoli.
Breathing in- Diaphragm muscles and external intercostal muscles contract. Volume increases and pressure decreases in thoracic activity. Air moves down a pressure gradient.
Breathing out. Diaphragm muscles relax and internal intercostal muscles contract. Volume decreases and pressure increase in thoracic activity. Air moves up along concentration gradient
Tidal volume is..
volume of air in each breath
