Introduction

Germination is the sprouting of a seed.  When germination begins the seed needs a lot of water.  The water makes a chemical change that enables the embryo to store food and energy for growth.  The water also causes the baby seed (“embryo”) to enlarge and split the seed coat.  Germinating seeds require a large amount of oxygen and give off carbon dioxide.  One part of the embryo, called the radicle, comes out and grows making the roots.  Another part, called the plumule, turns into the shoot of the plant.  The endosperm is the food store that surrounds the baby plant.

Common bean

After the shoot and roots become visible the first plant part you see is called the cotyledons.  They help feed the new seedling until it can make its own food.

Plant Food

All plants require food.  The food is also call nutrients.  Macronutrients are needed in large quantities (such as carbon, oxygen, nitrogen and phosphorus).  Micronutrients like iron, copper, manganese, boron and zinc are needed in small amounts.  Three important nutrients are nitrogen, phosphorus, and potassium.

Nitrogen is very important and has to be converted to nitrate by the bacteria that live on roots and in the soils.

The Nitrogen Cycle is very important to plants. Nitrogen is a major component of amino acids, proteins, and chlorophyll present in plants and is needed for plants to live.

Fertilizers were made to supply plants with any nutrients that they are short of to stimulate growth and are made of nitrogen, phosphorus and potassium.

How to Grow Plants

1.     Allow room to grow so pick the right sized pot.

2.     Don't put too many plants in it. 

3.     Keep them warm.  Plants grow best if the temperature does not go below 12°C or above 24°C.

4.     Plants can grow in lots of different kinds of light.  Some need shade but most love sunlight the best.  Give those plants 7 to 12 hours of strong light each day.  Plants make their own food because they have chlorophyll.  Photosynthesis is the chemical change that produces food for the plant.  In photosynthesis, carbon dioxide, gas and water are mixed to make sugar and oxygen.  Sunlight is the energy it needs to make the chemical reaction.

5.     Water your plants only when they need it.  If roots are not given enough water, the plants will wilt and die.  If the roots are given too much water they will rot and the plant will also die. 

6.     Plants don't breathe like people, but they do take up air through their leaves and roots.

7.     Plants take up food from the soil (called nutrients) to help them grow strong.

8.     Care for your plants and be patient, plants need time to grow.

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Soil pH

Soil pH or soil reaction is an indication of the acidity or alkalinity of soil and is measured in pH units.  The pH scale goes from 0 to 14 with pH 7 as the neutral point.  From pH 7 to 0 the soil is increasingly more acidic (eg. soda = 2 – 4) and from pH 7 to 14 the soil is increasingly more alkaline (eg. borax = 9).  Most minerals and nutrients are more soluble in acid soils than in slightly alkaline soils.

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Plant Cell Types

Plant cells help the plant grow.  Parenchyma tissue is made up of thin-walled cells that store water and salt.  Xylem tissue is made up of thick-walled cells that transport water and dissolved minerals from the roots up through the stem to the different parts of a plant.  Phloem tissue contains living cells that transport food produced throughout the plant.  Collenchyma tissue has thick walls for added strength and support.  Meristematic cells give rise to all three fundamental mature cell types. Their major function is cell division.

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Plant Hormones

Plant growth is controlled by growth hormones such as auxins, cytokinins, gibberellins (GA), and abscisic acid (ABA).  Water stress, the lack of water, decreases auxin and increases abscisic acid.  Auxins are involved in the growth of all parts of the plant, and abscisic acid is an inhibitor that may be involved in inducing dormancy.  Pruning is a stress because hormones made by buds are not present.  The result is the cytokinin to auxin ratio is high which produces unusual growth.  Sometimes plants grow better because of this.  Sometimes stress is helpful.  For example, at the end of summer, the changes in temperature, light and moisture change the hormone balance in plants causing the plant to enter dormancy long before the frost comes protecting plants from frost.  Sometimes stress is harmful and the plant does not thrive.

The stimulating hormones (auxin, cytokinin, and brassinosteroid) generally suppress the effect and production of the inhibiting hormones (ABA, ethylene, and GA) and vice versa.

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Salicylic Acid (SA)

Salicylic Acid naturally occurs in plants in very low amounts.  It is also manufactured and used to make Aspirin tablets.  Evidence has been found that shows Salicylic Acid can stimulate flowering.  Also, Salicylic Acid has been found to cause temperature increases of as much as 14ºC above the ambient temperature in the Arum group of plants (eg. duckweed, Skunk Cabbage).  Salicylic Acid is thought by some people to be a new plant growth hormone.  Also, some people use Aspirin in cut flowers to make the flowers last longer.

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References

(1)  Phyllis J. Perry, Science Fair Success with Plants, Enslow 1999

(2)  Robert W. Wood, Science for Kids, Tab 1991

(3)  Biological Sciences in Middle East Technical University

(4)  ENCYCLOPÆDIA BRITANNICA

(5)  MadSci Network: Agricultural Sciences

(6)  Botany online University of Hamburg
http://www.rrz.uni-hamburg.de/biologie/b_online

(7)  Cornell University College of Agriculture and Life Sciences

(8)  Ellen Silva, Originally published as "Plant Stress Management,"  

Extension Technician, Department of Horticulture, in 

The Virginia Gardener Newsletter, Volume 10, Number 4.

(9)  Kimball's Biology Pages    http://www.ultranet.com/~jkimball/BiologyPages/  

(10) Santiago Ortiz - FLASH 5 - my modifications and use in Virtual Garden 

approved 

(11) Prof R. Koning, PhD Botany

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