arif ullah iths - 01817721521j) limiting factors and ... · organic substances. these are called...

INTERNATIONAL TURKISH HOPE SCHOOL-CHITTAGONG BRANCHBIOLOGY HANDOUT 2014 - 2015: CLASS ……

TOPIC: PLANT NUTRITION

Teacher in Charge: ARIF ULLAH - 01817721521 1

Nutrition in Plants:a) Photosynthesis.b) Factors affecting photosynthesis rate.c) Experiments to prove the factors affecting photosynthesis rate.d) Autotrophs vs. heterotrophs.e) Adaptation of a leaf for photosynthesis.f) Fate of glucose in a leaf.g) Importance of destarching a plant.h) Testing a leaf for starch.i) Mineral Nutrition in Plants.j) Limiting factors and control for experiments.

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Introduction to the topic:

Organisms obtain food in various ways to survive and carry out physiologicalprocesses like respiration, growth, and osmo-regulation. Organisms that havechlorophyll (green pigment) such as plants and protests (i.e. Euglena) make foodby combining inorganic substances namely water and carbon dioxide to makecarbohydrates in a process called photosynthesis. This process involves the use ofenergy (solar energy) from the sun. Some use energy from the oxidation ofcertain substances to make food in a process called chemosynthesis. Organismsthat make their own food are referred to as autotrophs.

Some organisms obtain complex food substances made by other organisms andbreak them down to simple substances while others make their own food fromsimple inorganic substances. Some organisms obtain food by breaking down deadorganic substances. These are called saprophytes and the type of feeding is calledsaprophytism. For example, fungi feed on a dead decaying wood. Therefore,fungi are saprophytes. Some organisms obtain food by associating with otherorganisms in particular kinds of relationships. Organisms that obtain food byassociating with others of not their own kind, is a relationship called parasitism. Inthis relationship, the organism that benefits is called a parasite while the otherthat does not benefit (may be harmed) is called a host e.g a tick on a cow. In otherrelationships, both organisms benefit from the relationship. This is calledmutualism e.g the gut bacteria. In some relationships, one organism may benefitor not. This is called commensalism and the organisms involved are calledcommensals. All relationships where two organisms live together are calledsymbiosis.

Organisms which obtain food by breaking down complex food substances tosimple absorbable molecules are called heterotrophs.

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Photosynthesis:

The process by which plants make their own food (glucose) by combining carbondioxide and water, in the presence of sunlight and chlorophyll, giving oxygen as abi product.

Chemical equation of photosynthesis:

Word equation for photosynthesis:Water + carbon dioxide Glucose + Oxygen

Balanced chemical equation for photosynthesis:

Photosynthesis is Anabolic (glucose is built)Respiration is Catabolic (glucose is broken down)

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Factors affecting photosynthesis rate:It can be affected by many things, including:1) Sunlight - its Intensity & wavelength.2) Temperature3) CO2 and O2 – availability4) Any factor that influences the production of chlorophyll, enzymes, or energycarriers (ATP and NADPH).

The rates of photosynthesis will always correspond to that factor which is in leastsupply. Their rates will only increase when its supply is increased.

Sunlight

Generally the more light there is, the more photosynthesis occurs. This is true upto a point, where the plant has reached maximum photosynthesis levels, and soany increase in light intensity will not affect the plant further.

Temperature

Generally higher temperatures are better than cold temperatures forphotosynthesis. However if it is humid, and the air is saturated with water vapor,photosynthesis is limited. This is because the water vapor being expelled cannotleave and go into the air, as there isn't a concentration difference for it to diffuseacross. So the water vapor sits in the leaf, stopping photosynthesis.

CO2Basically the more CO2 in the air, the better the rate of photosynthesis. Of courseCO2 is taken in during the daytime, and if its content was less than normal,photosynthesis couldn't happen normally. Fertilizers increase the number of soilfungi and bacteria, thus increasing the levels of CO2 from their respiration anddecomposition processes. So fertilizers are good news for plants.

Water

Plants need water for photosynthesis. If they lack it, they wilt. When they have adeficiency of water, their stomata close, so CO2 cannot diffuse into the leaves. SoCO2 is also the limiting factor, although it is as a result of lack of water.ARIF U

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Experiments to prove the factors affecting photosynthesis rate:

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Aim: To show that light is necessary for photosynthesis.

Apparatus and Materials: well watered destarched potted plant, dark paper,scissors / knife / scalpel, pins/clips

Method/procedure:The set up is as shown below:

- Fix the paper on one of the leaves as shown in the diagram below.Diagram to show the set up.

- The experimental set up is exposed to sunlight for 2-6 hours.- The paper is removed and the leaf is tested for starch.ARIF ULL

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Results.

Diagram showing results. (the parts that were covered are stained brown, and therest of the leaf turns blue or black)

Conclusion.Starch is produced only in areas that received light, showing thatlight is necessary for photosynthesis.

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Autotrophs vs. Heterotrophs:

Heterotrophic means obtaining readymade organic food from the environmentand Autotrophic means manufacturing food from inorganic compounds usuallycarbon dioxide, water using a source of energyAutotrophic nutrition is a process where plants make food by combining largecomplex organic molecules such as starch, lipids and protein with simple inorganicmolecules like water, carbon dioxide and minerals.Example: plantsHeterotrophic nutrition is where organism feed on organic substances that havebeen made by other organisms.Examples are animals and fungi.

STOMATA (Space between two Guard Cells)

Guard cells are the only epidermal cells which can make sugar. In sunlight the concentrationof potassium ions (k+) increases in the guard cells. This, together with the sugars formed,lowers the water potential in the guard cells. As a result, water from other cells enters theguard cells by osmosis so they swell and become turgid. Because the guard cells have athicker cellulose wall on one side of the cell, i.e. the side around the stomatal pore, theswollen guard cells become more curved and pull the stoma open. At night, the sugar isused up and water leaves the guard cells, so they become flaccid and the stomatal porecloses. In this way, they reduce the amount of water vapour escaping from the leaf.ARIF U

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Adaptations of a leaf for photosynthesis:

Cuticle: - Is non-cellular, water proof and transparent. It allows light to passthrough.Upper epidermis: - Is a single layer of cells on the upper surface of a leaf. Itallows light to pass to the cells below.Palisade mesophyll - has cells vertically arranged such that many can fit intoa small space. The cells have large number of chloroplasts.Chloroplasts: - contain chlorophyll for absorbing sunlight.Spongy mesophyll: - Have large air spaces for fast diffusion of gases to andfrom the photosynthesizing cells. The cells have few chloroplasts.Veins (Vascular bundles): - They act as drain pipes distributing rawmaterials to the leaves and conducting away manufactured food to otherparts of a plant.Stoma: - A pore that allows gaseous exchange to take place. Carbon dioxideenters and oxygen leaves the leaf through stomata.Thin lamina: - Provides a short distance over which diffusion of gases takeplace.Broad lamina: - Provides a large surface area for absorbing sunlight energy.

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Fate of glucose in green plants:Stored as starch: Glucose is converted into starch and is transported away to bestored in roots, stem and leaves.Stored in seeds: Fats and oils commonly known as lipids found in seeds are madefrom glucose.Used to make fruit: Glucose may be used to make other sugars, such as sucrosefor storing in fruits.Used to make proteins: Nitrates from the soil combine with glucose to makeamino acids which are then put together to make proteins.Required for transport: Glucose is used to make energy, which is required totransport substances around the plant, especially for ACTIVE UPTAKE of mineralsin the roots.Used to make cell walls: Glucose is used to make other organic substances, suchas cellulose for making cell walls, particularly in fast growing plants.Used for respiration: Plants make glucose in the leaves. Some of that is usedstraight away for respiration to get energy, which is then used to convert rest ofthe glucose together with minerals from the soil into many other usefulsubstances.

Importance of destarching a plant:A plant is placed in dark for 24 hours.This prevents photosynthesis and uses up all the stored starch for respiration.Hence, no starch will be present at the beginning of the experiment.If photosynthesis occurs, starch would be present at the end of the experiment.

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Mineral nutrition in plants:

Table:Macroandmicronutrientsandtheiruses.

Mineral salts are necessary for normal plant growth.Several elements are known for normal plant growth and development.Some of these elements are Carbon, Hydrogen and Oxygen.Other elements are Nitrogen, Sulphur, Phosphorus, Potassium, Calcium andMagnesium.

Macro nutrients Uses DeficiencyNitrogen Amino acid and protein synthesis - Chlorosis with purple

colouringsPhosphorus Protein formation - Reddish purple leaves

and stunted growth.Sulphur Formation of certain amino acids - Stunted growth

- yellow patches onleaves

Calcium Formation of cell wall (middlelamella)

- Poor development ofleaves at shoot apex

Potassium Concerned with synthesis ofcarbohydrates and proteinmetabolism in young leaves.

- Chlorosis, andyellowing of leaves atthe margins, tips.- Retarded growth.

Magnesium Chlorophyll formation. Facilitatesenzyme activity.

- Chlorosis of olderleaves. - Stuntedgrowth.

Iron Required for the formation ofchlorophyll but not part of themolecule.

- Chlorosis with paleleaves

MicronutrientsCobalt, Copper,Zinc, Manganese,Boron

They are necessary for themanufacture of enzymes.

- Stunted growth ofleaves.

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Alternative to Fertilizers, for increasing crop yield:1. Crop Rotation - Growing leguminous plants, i.e. Nitrogen Fixing bacteria

residing in the root nodules of the roots. Eg.2. Using Green houses i.e. Glass Houses with appropriate conditions for plants

growth with enough sunlight, CO2, H2O and Temperature.

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Limiting factors for photosynthesis:1) After increasing light intensity, the rate of photosynthesis increases.2) The rate of photosynthesis reaches its highest peak.3) After that, the rate of reaction becomes constant.

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ARIF ULL

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arif ullah iths - 01817721521j) limiting factors and ... · organic substances. these are called...

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