2) Structure and functions in living organisms - transport Flashcards
(42 cards)
Why unicellular organisms can rely on diffusion for movement of substances in and out of the cell
-have very large surface area: volume
-do not need to have specialist exchange surfaces or transport systems
-diffusion is fast due to short distances required for substances to travel
Need for transport system in multicellular organisms
-small SA:vol
-distance between the surface of the organism to its centre is relatively long
-diffusion, osmosis and active transport cannot occur at a sufficient rate
Phloem function
-transport food materials (mainly sucrose and amino acids) made by the plant from photosynthesising leaves to non-photosynthesising regions in the roots and stem
-movement can be in any direction around the plant
Phloem structural features
-cells are living cells, not hollow
-substances move from cell to cell through pores in the end walls of each cell
Xylem function
-transport water and minerals from the roots to the stem and leaves
Xylem structures
-composed of dead cells which form hollow tubes
- strengthened by lignin
Root hair cells
Adapted for the efficient up take of water by osmosis, and mineral ions by active transport
-single-celled extensions of epidermis cells in the root
-increase SA:vol
Uptake of water by the root
High proportion of dissolved minerals and sugars in the cytoplasm give it a low water potential - water moves into the root hair cells by osmosis
root hair cell –> root cortex cells –> xylem –> leaf mesophyll cells
Transpiration
Loss of water vapour from the parts of the plant that are above ground
1. evaporation of water at surfaces of spongy mesophyll cells - has air spaces which creates a large surface area
2. diffusion of water vapour through the stomata as there is a concentration gradient
Process/ effect of transpiration
- Evaporation creates a slight shortage of water in the leaf so more water is drawn from xylem to replace it
- this draws more water from roots, and there is a constant transpiration of water through the plant
-water molecules pull each other up the xylem as they are cohesive
Need for transpiration
-transporting mineral ions
-providing water to keep cells turgid - support strucutre
-provide water to leaf cells for photosynthesis
-keep leaves cool - use of heat energy to convert water into water vapour as it leaves the plant helps to cool the plant down
Factors affecting rate of transpiration
-wind speed
-humidity
-light intensity
-temperature
Factors affecting rate of transpiration - wind speed
If higher, transpiration higher
-airflow removes water vapour from the air surrounding the leaf
-increases concentration gradient between the leaf and the air
-increases water loss
Factors affecting rate of transpiration - humidity
If higher, more transpiration
-concentration gradient is weaker
-less water lost
Factors affecting rate of transpiration - light intensity
If higher, more transpiration
-guard cells become turgid, stomata open
-allow water to be lost
Factors affecting rate of transpiration - temperature
If higher, more transpiration
-particles have more kinetic energy
-water molecules evaporate from the mesophyll
-diffuse away faster than at low temperatures
Practical: Factors Affecting Transpiration - mass potometer
- Set up a potometer.
- Set up the necessary environmental factors
- Temp: use a temperature-controlled room or water bath
- Humidity: Wrap the shoot in a plastic bag with varying degrees of vapour.
- Wind speed: fan
- Light intensity: lamp - Allow time for the apparatus to equilibrate.
- Record the starting position of the air bubble in the capillary tube.
- Leave for 1 hour.
- Record the final position of the air bubble
- calculate distance moved, and volume of water absorbed by the plant
- Repeat steps 1-7, changing the factor at fixed intervals
Composition of blood
-consists of red blood cells, white blood cells, platelets, plasma
-55% - plasma
-1% - white blood cells and platelets
-45% - red blood cells
Role of plasma
-mostly water
-other substances dissolved:
-nutrients - glucose, waste products, urea, CO2
-transport heat energy from respiring tissues
-protein molecules (plasma proteins) that remain in the blood all the time
-hormones
Red blood cells (erythorcyte)
Specialised cells which carry oxygen to respiring cells
Adaptations of red blood cells
-full of haemoglobin - protein that binds to oxygen to form oxyhaemoglobin
-no nucleus - allows more space for haemoglobin to be packed in
-bioconcave disc shape - gives large SA:vol to maximise diffusion of oxygen in and out
White blood cells
-part of the body’s immune system
-specialised cells defend against pathogenic microorganisms
-two types:
-phagocytes
-lymphocytes
Phagocytes
- have a sensitive cell surface membrane that can detect chemicals produced by pathogenic cells
- Once they encounter the pathogenic cell, they will engulf it and release digestive enzymes to digest it - phagocytosis
-non-specific immune response
Lymphocytes
- produce complementary antibodies (soluble proteins that pass into the plasma) Pathogens have chemical markers (antigens) on their surfaces, which antibodies recognize.
- Antibodies attach to the antigens and clump them together
- Act as a label on the pathogen, so that it is more easily recognized by a phagocyte
- produce antitoxins to neutralize toxins released by pathogens
-production of antibodies after the first exposure - primary immune response
