nutrition in plants

function of lamina (leaf blade)

provides a surface area for absorption of light energy and for gaseous exchange

lamina thin, relation to function?

lamina is thin, leaf allows carbon dioxide to reach inner cells rapidly and enables light to reach ALL mesophyll cells

function of network of veins

contains a vascular bundle of the lead to transport water, mineral salts and manufactured food

function of leaf stalk

to hold the lamina away from the stem so that the lamina can obtain sunlight and air, and allow water and mineral salts to be transported to the leaf, and manufactured food away from the leaf

parts of tissue level structure

cuticle, upper epidermis, palisade mesophyll tissue, spongy mesophyll tissue, vascular bundle (containing xylem and phloem), air spaces, guard cell, stoma and lower epidermis

what is cuticle and its function

it’s a thin, waterproof and transparent layer on upper and lower epidermis. it reduces excessive water loss due to evaporation and allows light to pass through to enter the leaf.

what is epidermis and its function?

epidermis is a one cell thick layer, and epidermal cells does not contain any chloroplast. it protects the leaf by preventing bacteria and fungi from getting in and reduces water loss from evaporation

what is palisade mesophyll tissue and its function?

cells are long and cylindrical, that are closely packed to maximise the number of cells in the tissue. these cells contain the most number of chloroplast, as it’s the main site of photosynthesis and more light can be absorbed at the upper surface of the leaf

what is spongy mesophyll tissue

cells have irregular shape, are: 1. loosely packed 2. surrounded with large intercellular air spaces in between 3. contains few chloroplasts 4. mesophyll cells are covered with a thin film of moisture

function of spongy mesophyll tissue?

thin film of moisture - allows water to exit mesophyll cells, allow oxygen and carbon dioxide to diffuse in the thin film of moisture for the diffusion of gases in and out of the mesophyll cells. intercellular air spaces - allows diffusion of oxygen, carbon dioxide and water vapor within the leafy allows diffusion of oxygen and carbon dioxide in and out of the mesophyll cells for photosynthesis

stomata more commonly found where?

stoma are more commonly found on the LOWER surface of the leaf, to reduce the excessive water loss due to the less direct exposure to sunlight

presence of sunlight, what happens to guard cells and stoma?

rate of photosynthesis is higher and glucose concentration in guard cells increase, causing water potential of the cell sap of guard cells to decrease. there is higher water potential in the cell sap of surrounding mesophyll cells compared to guard cells. so water enters the guard cells by osmosis and guard cells become turgid, and more curved. this causes stoma to open.

hot sunny day, what happens to guard cells and stoma?

excess evaporation of water causes guard cells to become flaccid. this causes stomata to close, preventing excessive loss of water by leaves

how does carbon dioxide enter the leaf?

during the day, when photosynthesis occurs, carbon dioxide is used up in the leaf. carbon dioxide diffuses from a higher concentration in the surrounding air to a lower concentration inside of the leaf. carbon dioxide dissolved in the thin film of moisture on the surface of mesophyll cells. the dissolved carbon dioxide then diffuses into the cells.

function of xylem

1. transports water and mineral salt ions upwards from the roots of the leaves 2. provides mechanical support for the plant

function of phloem

transports manufactured food substances bidirectionally from the leaves, to the rest of the plant

what’s the layer between xylem and phloem and what does it do?

the layer between xylem and phloem is called cambium! it forms stem cells, similar to bone marrow in humans.

specialisation of xylem and relation to function (xylem)

1. hollow vessel made of only the cell wall and no organelles, (also has no cross walls) - this allows water and mineral salt ions to move through the xylem without any resistance 2. cell walls are thickened with lignin - lignin increases the strength of the cell wall for support to prevent them from collapsing

phloem cells contain 2 other cells too! what are they?

sieve tubes and companion cells

specialisation of phloem and relation to function (phloem)

1. sieve tube cell has only a thin layer of cytoplasm, and sieve plate have holes - this allows rapid flow of manufactured food substances through the phloem 2. companion cells have many mitochondria - this provides energy for active transport of manufactured food from the mesophyll cells into the sieve tubes

difference between companion cells and sieve tube cells (hint: related to what cell organelles each cell has)

companion cells have the usual cell organelles including mitochondria. sieve tube cells do NOT have most cell organelles, like ER and nucleus

xylem and phloem, wall thickness differences?

xylem has thicker walls, phloem has thinner walls

xylem and phloem, lumen size differences who?

xylem has larger lumen, phloem has smaller lumen

definition of photosynthesis

photosynthesis is the process where carbon dioxide and water turns into glucose and oxygen, in the presence of light energy and chlorophyll. light energy converts to chemical energy.

enzymes effect on photosynthesis?

photosynthesis reaction is catalyses by enzymes!

fate of FREAKING glucose

glucose can be used for: 1. tissue respiration - where it’s energy for metabolism and active transport 2. transported as sucrose - stored in organs (fruits) as SUCROSE 3. transformed into other bio molecules - cellulose for cell wall, amino acids for proteins, fats for plasma membrane

how to determine rate of photosynthesis (carbon dioxide)

measure decrease in carbon dioxide concentration using a hydrogen carbonate indicator, colour of indicator can be used to determine the concentration, observe the change in colour over fixed time

how to determine rate of photosynthesis (oxygen)

measure volume of oxygen produced over fixed time using a gas syringe OR by counting the number of oxygen bubbles produced over fixed time

how to determine rate of photosynthesis (glucose)

use iodine test on decolorised leaf. detailed version - 1. need to destarch plant by putting in the dark for 48 hours (no photosynthesis can occur, no starch produced) before testing for starch 2. place leaf in boiling water for 5 mins to kill the leaf and stop chemical reactions 3. place leaf in boiling tube containing ethanol, then place boiling tube in hot water for 5 mins. this is to decolorise leaf by removing chlorophyll so that colour change can be observed easily 4. remove decolorised leaf and wash it with warm water then do the iodine test (FREAKING finally)

factors of photosynthesis

light intensity, carbon dioxide concentration and temperature

how to vary factors of photosynthesis

increase/decrease distance of lamp from set up, use a thermostat to control temp of water, pump more carbon dioxide into set up