b2 Flashcards
(36 cards)
Factors affecting diffusion
Conc gradient
Temp
SA
Mitosis
Stage 1 (Interphase): In this stage the cell grows, organelles (such as ribosome and mitochondria) grow and increase in number, the synthesis of proteins occurs, all 46 chromosomes are replicated (forming the characteristic ‘X’ shape) and energy stores are increased
Stage 2 (Mitosis): The chromosomes line up at the equator of the cell and spindle fibres pull each chromosome of the ‘X’ to either side of the cell.
Stage 3 (Cytokinesis): Two identical daughter cells form when the cytoplasm and cell membranes divide, each containing the same 46 chromosomes as the original cell.
Cell division by mitosis in multicellular organisms is important in their growth and development, and when replacing damaged cells. Mitosis is also a vital part of asexual reproduction, as this type of reproduction only involves one organism, so to produce offspring it simply replicates its own cells.
Root cell adaptations
Large SA, more water can move in
Large permanent vacuole, speed of movement of water from soil to cell increases
Lots of mitochondria to provide energy for respiration for active transport
Meristems
Found in root and shoot tips
• They can differentiate into any type of plant, and have this ability throughout the life of the plant
• They can be used to make clones of the plant- this may be necessary if the parent plant has certain desirable features (such as disease resistance), for research or to save a rare plant from extinction
Transpiration
Transpiration is the loss of water of water vapour from the leaves and stems of the plant. It is a consequence of gaseous exchange, as the stomata are open so that this can occur.
• Water also evaporates at the open stomata
• As water molecules are attracted to each other, when some molecules leave the plant the rest are pulled up through the xylem
• This results in more water being taken up from the soil resulting in a continuous transpiration stream through the plant
Xylem adaptations
A chemical called lignin is deposited which causes the cells to die.
• These cells then become hollow and join end-to-end to form a continuous tube for water and mineral ions to travel through from the roots
• Water molecules are attracted to each other by hydrogen bonding - creating a continuous column of water up the plant
• The water evaporates from the leaves of the plant, creating the transpiration stream.
• Lignin strengthens the plant to help it withstand the pressure of the water movement
• Lignin contains bordered pits, which are holes to allow specific areas for water and therefore minerals to enter the plant
Guard cells
Open and close stomata
• They are kidney shaped, with thin outer walls and thick inner walls
• When lots of water is available to the plant, the cells fill and change shape, opening stomata (they are also light sensitive)
This allows gases to be exchanged and more water to leave the plant via evaporation
More stomata are found on the bottom of the leaf, allowing gases to be exchanged whilst minimising water loss by evaporation as the lower surface is shaded and cooler.
Factors affecting water uptake
Light intensity
Temp
Air movement
Humidity (decrease- reduced conc gradient)
Potometer experiment
A potometer can be used to investigate how these factors affect water uptake. It is set up underwate remove air bubbles in the xylem so that there is a continuous stream of water and the system made airtight, apart from a singular bubble of air. The distance this air bubble in the capillary tube moves over time is measured. If it moves faster then it means that there is a greater rate of water uptake and therefore rate of transpiration. An environmental condition, such as light intensity, is changed each time the experiment is run in order to see how it affects the plant.
Phloem adaptations
Found in the roots, stems and leaves
• Elongated cells with holes in the cell walls (the end walls are called sieve plates)
• Many organelles from the cells are removed so cell sap can move through.
• However, there are many mitochondria in companion cells which provide the energy cells require
• Food substances can be moved in both directions (translocation), from the leaves where they are made for use, or from storage (underground) to parts of the plant that need it.
What happens when a plant cell is placed in surroundings less concentrated than cell contents
Takes up water by osmosis. Pressure in cell increases (turgor pressure). Cell becomes firm or turgid
What happens when plant cell is placed in surroundings more concentrated than cell contents
Loses water by osmosis
Turgor pressure falls
Becomes flaccid (soft)
Eventually the cell contents collapse away from the cell wall.
Plasmolysed cell
What happens when animal cells are placed in surroundings less concentrated than cell contents
Takes up water, swells, and may burst
Lysis
What happens when animal cells are placed in surroundings more concentrated than cell contents
Loses water by osmosis
Becomes crenated
3 key features of active transport
Particles transported against conc gradient
ATP needed, comes from respiration
Makes uses of carrier proteins
What are carrier proteins
Span across the width of the cell membrane
A particular molecule a cell needs binds to the carrier protein
Energy is transferred from an energy store to the protein so that it can change shape or rotate
Carrier protein transports the molecule into the cell
Active transport in digestive system
In small intestine, carbs are broken down into glucose.
Glucose is actively transported into bloodstream thru villi.
Blood takes glucose to where needed in body.
Active transport in nerve cells
Carrier protein actively pumps sodium ions out of the cell
At the same time potassium ions are pumped back in
Sodium potassium pump plays important role in creating nerve impulss
Active transport in nerve cells
Carrier protein actively pumps sodium ions out of the cell
At the same time potassium ions are pumped back in
Sodium potassium pump plays important role in creating nerve impulses
Active transport in plants
Use AT to take in minerals from soil
Root hair cells use active transport to move ions with low conc in soil into the plant across the membrane
Specialised cells- sperm cell
Flagellum (tail)- propels sperm to the ovum
Lots of mitochondria- respiration, so energy provided for flagellum to move
Acrosome- stores digestive enzymes, which break down outer layer of ovum so sperm can incorporate genetic material
Specialised cells- fat cell
Small layer of cytoplasm surround fat reservoir- can expand up to 1000 times their original size as they fill with fat
- what is a function of carrier proteins in a cell membrane
transfer molecules by active transport
why might you used embryonic stem cells over adult stem cells
able to differentiate into any cell
adult stem cells are limited
