Plants Flashcards
Cuticle structure & function
Waxy and transparent, no chloroplast, reduces water loss through evaporation from leaf and prevents invasion of bacteria or viruses
Epidermis structure & function
Single layer of closely packed cells, covered on outside with cuticle, protects inner cells and allows light to pass through
Palisade mesophyll structure & function
Long and cylindrical, contain largest number of chloroplasts to absorb light energy for photosynthesis. Nearest to upper epidermis and closely packed.
Spongy mesophyll structure and functions
Irregularly shaped cells which contain chloroplasts, loosely packed with large intercellular air spaces among cells to increase surface area for gaseous exchange covered with thin film of moisture and contain vascular bundle
Vascular bundle structure and functions
Contains xylem and phloem, xylem transports water and mineral salts to mesophyll cells and phloem transports sucrose and amino acids away from leaf to other parts of plant
Large intercellular air spaces functions
Allow circulation of air inside leaf for photosynthesis and respiration, interconnecting system of air spaces allow rapid diffusion of CO2 and O2 into and out of cells
Guard Cells functions
Contain chloroplasts and regulate size of stomata for gaseous exchange and transpiration, cell wall near stoma is thicker.
Reason for stomata being present
Open in presence of light, allowing carbon dioxide to diffuse in and oxygen to diffuse out of leaf
Reason for more chloroplasts in upper palisade tissue
More light can be absorbed near leaf surface for photosynthesis
Reason for chloroplasts containing chlorophyll
Chlorophyll absorbs energy from sunlight and transfers it to chemical stores of energy in glucose molecules
How do guard cells control size of stomata in day
Guard cells photosynthesise, chemical energy pump K+ into guard cells from neighbouring epidermal cells, conc of K+ ^ in guard cell, water potential lowered, water from neighbouring cells enter guard cells by osmosis, guard cells swell and become turgid, due to difference in thickness of cell wall, one side expands more than other, stoma opens
How do guard cells control size of stomata in night
K+ move out of guard cells via diffusion, water potential in guard cell decreases, water moves out of guard cells by osmosis, become flaccid, stoma closes
Use of stomata in gaseous exchange
Allows exchange of CO2 and O2 with atmosphere
Use of vascular bundles in transport
Network is extensive, provides effective transport of water and mineral salts from roots to leaves through xylem and sucrose and amino acids away from leaves to other parts of plants
Definition of cambium
Contains undifferentiated cells which can divide to form new phloem and xylem
How are xylem vessels formed
When cells, arranged end-to-end are matured and cross wall in adjacent cells is removed. Cell membranes and cellular contents break down, forming long continuous and hollow tubes
Structural adaptation of xylem
Empty lumen, consisting of dead cells, reduces resistance to flow of water
Use of inner walls of xylem being strengthened by lignin deposits
Provides mechanical support for plant, prevents collapse of vessel and allows it to provide mechanical support to plant
Define translocation
Process of transporting manufactured food substances such as sucrose and amino acids in phloem
Structure of phloem
Composed of sieve tubes, columns of specialised cells called sieve tube cells, individual sieve tube cells are separated by perforated walls(sieve plates)
Reasons for sieve tube cells living with reduced quantities of cytoplasm, no nucleus and presence of sieve plates
Sieve tube cells must be living as translocation is active process sieve plates with reduced cytoplasm means resistance to flow of food substances is reduced
Reasons for companion cells containing many mitochondria
Perform many genetic and metabolic functions of sieve tube cells, keeping them alive. Mitochondria provide energy needed by sieve tube cells for translocation, used to load organic compounds at source
Why is translocation active process
Phloem must be able to transport substances in either direction as links parts of plant that need supply of sucrose and amino acids to other parts with a surplus.