Transport in Flowering Plants Flashcards
(33 cards)
what are the four structures of dicotyledonous?
- 2 cotyledons in embryo
- a network of veins in leaves
- flowers are in multiples of 4 or 5
- ring-like arrangement of vascular bundles in the stem
what is the structure of a xylem and their functions?
- xylem vessel is long and hollow, and made up of many dead cells without cytoplasm and cross-walls, hence reducing resistance of water and mineral salts flowing through the xylem from roots to leaves
- inner walls of the xylem vessels are thickened with lignin to strengthen and prevent the collapsing of walls
what is translocation?
the transportation of sucrose and amino acids in the phloem from the source to sink
what is the structure of the phloem and their functions?
- phloem vessel is found throughout the plant which facilitates translocation
- contains sieve tubes made of sieve tube cells separated by porous sieve plates for efficient movement of sucrose and amino acids flowing in the sieve tube
- companion cells are beside sieve tube cells as they have many mitochondria to facilitate the active transport of sucrose in and out of the sieve tube to carry out metabolic processes needed to keep the sieve tube cell alive
what is a structure of the sieve tube cells and its function?
sieve tube cells are alive but have no nuclei and reduced numbers of organelles to maximize space for the translocation of sucrose and amino acids
what is a structure of companion cells and its function?
companion cells have a continuous cytoplasm with the cytoplasm of sieve tube cells to facilitate the rapid movement of metabolites between the two types of cells
what is a source?
areas where sucrose and amino acids are loaded into the phloem
what is a sink?
areas where sucrose and amino acids are unloaded and used
what are the 3 main layers of a dicotyledonous stem?
- epidermis
- cortex
- pith
what is the arrangement of vascular bundles in a dicotyledonous stem?
- located next to the cortex of the stem
- arranged in a ring shape near the epidermis of the stem
- phloem vessels are closer to the epidermis while the xylem vessels are closer to the pith
what are the 4 main layers of a dicotyledonous leaf?
- upper epidermis
- palisade mesophyll
- spongy mesophyll
- lower epidermis
what are the 3 main layers of a dicotyledonous root?
- epidermis
- cortex
- endodermis
what is the epidermis of the root?
the outermost layer of cells that bears root hair cells
what is the structure of a root hair and its function?
each root hair is a long and narrow extension growing out of the epidermal cell which increases the surface area to volume ratio of the root hair cell, increasing the rate of absorption of water by osmosis and mineral salts by diffusion and active transport
what is the arrangement of vascular bundles in a dicotyledonous root?
- located in the middle of the root and surrounded by the endodermis
- xylem vessels are arranged in a cross shape
- phloem vessels are grouped into round areas surrounding the xylem vessels
what is the process of the aphid feeding experiment?
- while the aphid is feeding by having its stylet tip inserted into the phloem, anaesthetise it with carbon dioxide
- cut off the body of the aphid , leaving its stylet tip in the plant tissue
- collect the fluid from the stylet tip to reveal sucrose and amino acids
- section the stem and look at it under the microscope to show that the stylet tip is inserted into the phloem sieve tube
what is the process of the ‘ringing’ experiment?
- cut off the complete ring of bark from the main stem to expose the xylem
- prepare a control using an unringed stem
- observe for a few days to see if there is any swelling present
- swelling will be seen above the removed ring
- materials are accumulated above the removed ring, and collection of these materials reveal that they are sucrose and amino acids
what is the process of the 14C isotope experiment?
- plants are exposed to 14C isotope, a radioactive carbon isotope
- when photosynthesis takes place, the sugars formed will contain the radioactive carbon
- cut the stem and expose its cross section onto an x-ray photographic film where the radioactive carbon will appear dark on the x-ray film
what is transpiration?
the loss of water vapour from the thin film of moisture on the spongy mesophyll by evaporation, especially through the stomata
how does water enter from the roots?
- root hairs which are narrow extensions of an epidermal cell are in contact with the soil solution surrounding it, which is a dilute solution of mineral salts
- cell sap of the root hair cell has a lower water potential than the surrounding soil solution, hence a net movement of water molecules enters the cell by osmosis across the partially permeable cell surface membrane
- this dilutes the root hair cell sap, hence it has a higher water potential than the adjacent cortex cell, and water passes by osmosis from the root hair cell into the cortex cell
- the process continues until the water molecules enters the xylem vessels by osmosis and moves up the plant
what is transpiration pull?
the suction force caused by transpiration and serves as the main factor that causes movement of water and mineral salts up the xylem
what is the process of transpiration?
- water moves out of the mesophyll cell to form a thin film of moisture, where it evaporates to form water vapour in the intercellular air space
- water vapour diffuses through the stomata to the drier air outside the leaf
- as water evaporates from the thin film of moisture, more water moves out of the mesophyll cells to replenish it, causing the water potential of the mesophyll cell sap to decrease, becoming lower than that of its neighbouring mesophyll cell
- mesophyll cells draw water from cells deeper inside the leaf by osmosis
- mesophyll cells deeper in the leaf then draw water from the xylem by osmosis, creating a suction force which pulls the whole column of water up the xylem vessels
why is transpiration important?
- transpiration pull it is the main way water and mineral salts are drawn from the roots to the leaves
- evaporation of water at the leaves cools the plant, preventing it from being scorched by the sun
- water transported to the leaves is used for photosynthesis and replacing water lost by cells
- keeps the cells turgid and leaves spread out to maximize the absorption of sunlight
how to measure the rate of transpiration?
a potometer can be used to measure the rate of water absorption
