cytoplasm vacuole

Plants Cell

cell wall cell membrane

cell wall  freely permeable so it lets most of molecules to go through  osmosis does not occur cell membrane  beneath cell wall  selectively permeable

Water Relations of Plant - Turgor

plant cell put in distilled water  net water movement into the cell by osmosis plant cell contains solutes water potential lower than pure water vacuole and cytoplasm swells

cytoplasm is pushed against cell wall turgor turgor is present because: cell wall is rigid and strong, cell bursting is prevented hydrostatic pressure develops inside the cell

tendency of the cell to give out water increases water potential increases When

water potential of cell = water potential of water

Turgor occur (cell cannot take in any water) the cell is turgid

Water Relations of Plant - Plasmolysis

plant cell in concentrated solution The whole phenomenon is called plasmolysis and cell is plasmolysed net water movement out of the cell by osmosis flaccid cytoplasm shrink from cell wall

vacuole enlarged

Turgidity of Plant Cells

cell membrane separated cell wall cytoplasm from cell wall vacuole very small turgid cell (in hypotonic sol.) plasmolysed cell (in hypertonic sol) solution here is the same as the external solution

Cells in Different Solutions

Solution Concentration hypotonic hypertonic animal cells (e.g. RBC) haemolysis shrink plant cells turgid plasmolysis (cell is flaccid)

To Investigate the Effects of Sucrose Solution and Tap Water on Epidermal Cells of Red Onion Scale Leaf or

Rhoeo Discolor Leaf

fleshy scale leaf of red onion bulb forceps filter paper epidermis What do you observe when the epidermal strip is placed in the concentrated sucrose solution ?

Ans: The coloured cytoplasm shrinks.

fleshy scale leaf of red onion bulb forceps filter paper epidermis Explain your observation.

Ans: When the piece of epidermis is placed in concentrated solution, cells lose water by osmosis as the cells have a higher water potential than the sugar solution.

fleshy scale leaf of red onion bulb forceps filter paper epidermis What has happened to the cells in tap water ?

Ans: The coloured cytoplasm swells and cells become turgid.

fleshy scale leaf of red onion bulb forceps filter paper epidermis Explain your answer.

Ans: When the piece of epidermis is placed in tap water, cells gain water by osmosis as the surrounding tap water has a higher water potential than the cells.

Effects of Concentrated Sucrose Solution and Tap Water on Raw Potato Strips

petri dish 20% surcose solution water raw potato strips A B What has happened to the potato strips ?

Ans: Potato strip A increases in both weight and length while potato strip B decreases in both weight and length.

petri dish 20% surcose solution water raw potato strips A B Explain your answer.

Ans: For potato strip A, it gains water by osmosis so both of its weight and length increase but for potato strip B, it loses water by osmosis so its weight and length decrease.

Transpiration

 an evaporation of water in form of water vapour from the surface of plant to atmosphere  it mainly takes place in leaves where there are some openings called stomata

 more water loses from the lower surface of the leaf than the upper one as more stomata present on the lower surface  it also happens in lenticels and cuticle

Transpiration in Leaves

 a thin film of moisture is covered with each mesophyll cell  the moisture evaporates from mesophyll cells into intercellular spaces and diffuses out of stomata into atmosphere

 water potential of cells losing water decreases so they draw water from deeper cells in the leaf by osmosis. This in turn, draws water in xylem vessels into leaf to replace the loss

Experiment to Show that Water is Given Off During Transpiration

polythene bag A B What do you observe in the polythene bags ?

Ans: The one enclosing plant A becomes misty while nothing can be noticed in the one enclosing plant B.

polythene bag A B How can you show that it is water ?

Ans: We can use anhydrous cobalt chloride paper to test it. It will turn the paper from blue to pink or we can use anhydrous copper sulphate. Water will turn it from white to blue.

polythene bag A B What conclusions can you draw from the results ?

Ans: We can conclude that a leafy shoot gives off water during transpiration.

To Measure the Rate of Transpiration by Using a Simple Potometer

leafy shoot graduated capillary tube reservoir tap air/water meniscus What are the environmental conditions under which transpiration occurs quickly ?

Ans: It is under dry, warm and windy conditions.

leafy shoot graduated capillary tube reservoir tap air/water meniscus Does this apparatus give you an accurate measurement of the rate of transpiration ?

Ans: In addition, it is too small to fit the whole root system

leafy shoot graduated capillary tube reservoir tap air/water meniscus Sometimes you may introduce an air bubble into the capillary tube. State the advantage of this method.

Ans: Movement of the air bubble is easier to observe than that of air/water meniscus.

leafy shoot graduated capillary tube reservoir tap air/water meniscus Sometimes you may introduce an air bubble into the capillary tube. State the disadvantage of this method.

Ans: Friction between the capillary wall and the bubble may affect the movement of bubble.

Environmental Factors Affecting the Rate of Transpiration

There are five environmental factors which affect the rate of transpiration. They are: (I) Light Intensity (II) Temperature (IV) Wind Speed (V) Water Supply (III) Humidity

Light Intensity

 stomata open in light, so plants can get enough carbon dioxide from atmosphere for carrying out photosynthesis  light will increase temperature so increases the rate of transpiration

temperature

Temperature

rate of evaporation of water from mesophyll cells relative humidity of air outside leaf rate of diffusion of water vapour from intercellular space in leaf to outside

Humidity

 humidity outside rate of transpiration it makes the diffusion gradient of water vapour from moist intercellular space of a leaf to the external atmosphere steeper

Wind Speed & Water Supply

wind blows lack of water the leaf sweeps away and stomata close transpiration rate INCREASES transpiration rate DECREASES

Stomata

 stomata are pores in the epidermis which gaseous exchange takes place during photosynthesis (or respiration)  find mainly in lower epidermis of dicotyledonous leaves and stems

Guard Cells

 each stomata is surrounded by two guard cells which possess chloroplasts  its inner wall is thicker than outer wall  it is kidney-shaped guard cell stoma

Distribution of Stomata in Leaves

 normal plants  mainly on the lower surface of leaves  floating plants  mainly on the upper surface  leaves may also have air sacs to keep them afloat so they can carry out gaseous exchange

 submerged aquatic plants  no stomata (not required since gaseous exchange can be carried out by diffusion though the leave surface)  no cuticle (the primary function of cuticle is to prevent excess water transpiration which is not present in aquatic plants)

Experiment to Investigate Stomatal Distribution in a Leaf by Using Cobalt Chloride Paper

sellotape cobalt chloride paper Obtain a potted plant. Using sellotape stick a small square of anhydrous cobalt chloride paper onto each surface of a leaf of the plant. Record the time taken for the cobalt chloride paper on each surface of the leaf to turn pink.

sellotape cobalt chloride paper Which piece of cobalt chloride paper turns pink first? Ans: The piece of cobalt chloride paper attached to the lower epidermis of the leaf turns pink first.

sellotape cobalt chloride paper Explain your answer. Ans: It is because more stomata are present in the lower epidermis.

sellotape cobalt chloride paper Why is it important to handle cobalt chloride paper with forceps? Ans: It is because there is moisture on human fingers so the paper may turn pink before sticking onto the surfaces of leaves.

To Observe the Release of Air Bubbles from Leaves placed in Hot Water

forceps hot water leaf Which surface has more air bubbles coming off?

Ans: There are more air bubbles appear on the lower surface of the leaf.

forceps hot water leaf Where does the air come from?

Ans: It is in the air spaces between the mesophyll cells in leaf which expands on heating and passes out through stomata of the leaf.

forceps hot water leaf What does the result show?

Ans: The result shows that more stomata are present on the lower epidermis of the leaf.

 Root Cap

Structure of Root

 a protective layer at the very tip of root  to protect the delicate cells of root from being damaged as the root grows down through the soil  Epidermis  cover the rest of root  absence of cuticle so water can enter

 Growing Point  behind root cap  cells are capable of active division  Region of Elongation  more elongated than cells in growing point and have large vacuoles

 Region of Root Hair  little way behind root tip  root hair are thin-walled extension of epidermal cells of root  increase surface area for uptake of water and mineral salts

 Vascular Tissue  further from the tip of root  contain xylem and phloem  xylem transport absorbed water to every part of plant

Absorption of Soil Water by Root Hairs

 soil water is a dilute solution of salts which is more dilute than cell sap and cytoplasm in root hair  water will pass by osmosis into root hair through cell wall and cell membrane

transpiration occurs in leaves so water is continuously removed from the plant reduction of effective pressure at the top of xylem vessel water flows upwards from roots continuously flow of water through plant: transpiration stream tension produced to draw up water: transpiration pull

Transverse Transport of Water to Xylem

epidermal cells gain water by osmosis cytoplasm and cell sap have higher water potential than neighbouring cortical cells NOTE: some water may travel inwards along or between cell walls without entering cytoplasm or vacuole of each cortical cell water travels by osmosis inwards from cell to cell

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Functions of Transport System in Angiosperms

 carries water and mineral salts from the roots to the mesophyll cells of the leaves for photosynthesis by xylem

 carries foods made in the leaves by photosynthesis to other cells of the plant by phloem  xylem and phloem are together called vascular bundles

Arrangement of Conducting Tissues in Angiosperms

 in root - close to central position in which xylem is found in the centre in a star-like arrangement and phloem lies between the radial arms of the xylem

to resist the strong pulling force from the wind blowing the shoot  in stem - close to the epidermis where the conducting tissues are arranged in a ring near the outside edge, with phloem lying outside and xylem inside

- to resist the strong bending force produced by wind  in leaves - vascular bundles are often called veins in which xylem lies above the phloem

Xylem

 consists of long tubular vessels  each vessel is made up of many dead cells which are hollow and joined end to end

 the end walls of the cells have disappeared and so a long and open tube is formed  xylem vessels run from the root, through the stem and finally branch out into every leaf of the plant

 xylem vessels contain no cytoplasm or nuclei  to prevent xylem from collapsing, they have thick cell walls made of cellulose and strengthened by rings of a woody substance called lignin

Phloem

 made up of tube cells called sieve tubes which are living cells joined end to end by perforated horizontal walls called sieve plate  the perforations allow dissolved substances to flow through them so food made in the leaves can be carried to other parts of the plant

 sieve tubes contain cytoplasm but no nuclei and they do not have lignin in their cell walls  each sieve tube has a companion cell next to it. The companion cell does have a nucleus and contain many other organelles

Comparison between Sieve Tubes and Vessels

Sieve Tubes Vessels living cells smaller diameter walls relatively thin, flexible, composed of cellulose dead cells larger diameter walls relatively thick, hard, strengthened by rings of lignin

Comparison between Sieve Tubes and Vessels

Sieve Tubes Vessels the lumens of mature cells are filled with cytoplasm end walls of adjacent sieve tubes from sieve plates the lumens of mature cells are empty end walls of adjacent vessels cells break down

Upward Transportation of Water and Mineral Salts

• root pressure • capillarity • by transpiration pull

Transpiration Pull

 most of the water rising up in the xylem of the stem is pulled up by this  during transpiration, water is continually removed from the top of xylem vessels to supply cells in the leaves so pressure at the top of xylem reduces and water flows up

Transport of Organic Nutrients

 translocation is the process of transporting the manufactured carbohydrates in photosynthesis via phloem from the leaves to other parts of the plant

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