Plant Growth& Development

Necessities for Plants

• Plants require the following:– Water, carbon dioxide and light in order to run

photosynthesis and produce energy compounds (glucose).

– Inorganic substance (minerals) that assist in making larger organic molecules function properly.

– Favorable environmental conditions (precipitation, temperature, soil).

• If any one of these is in short supply, it acts as a limiting factor and will impede the development of the plant or cause it to die.

Soil & Soil Nutrients• The soil is important because it contains

many nutrients required for proper plant growth – both macro & micronutrients. – Macronutrients – these are substances

required in substantial amounts by the plant daily.•These include N, P, K, Ca & Mg

– Micronutrients – these are substances that are required in only small amounts daily.•These include Fe, Zn & Cu.

• Nitrogen is the most important nutrient. Plants rely on nitrogen fixation and soil bacteria (possibly in nodules) in order to gain their nitrogen.

Soil Layers• Soil has several

different layers:– Humus – Partially

decomposing plant and animal matter. (Called “litter” in grade 10.)

– Topsoil – Primary supporter of plant life.

– Subsoil – Soil layer that contains some rocks.

– Bedrock – Solid rock layer

Fertilizers Give Soil a Boost!• Fertilizers are mixtures that carry many

of the macronutrients needed for plant growth.

• Fertilizers may be organic (coming from a living source) or inorganic (produced chemically).

• Fertilizers often have a three number sequence on their containers such as 10-20-10. This is the proportionof macronutrients N-P-K in themixture.

• Do Discovering Biology – Pg. 560

Seed Dormancy• It takes a little more than just sticking a

seed into a hole and covering it over.• Seeds require the right environmental

conditions in order to start growing. If conditions are too harsh – the seed will remain in a state of dormancy.

• When conditions are good, the seed may come out of this period of dormancy and begin germination.

Inside the Seed• The embryo has

three parts – the radicle, hypocotyl and the epicotyl – the embryonic roots, stem and upper part of the plant respectively.

Germination• Germination is the development of the

embryonic plant after the seed has been “planted” and environmental conditions are favorable.

• The plant embryo, inside the seed, releases a hormone that breaks down the starch in the seed into a number of smaller glucose molecules.

• Water is brought in to balance out the glucose and the seed swells and cracks its seed coat.

• Oxygen can now get in and the embryo can start cellular respiration.

Germination

Plant Hormones and theControl of Plant Growth

Plant Hormones• First of all, a hormone is a chemical that is

produced in one part of the body that brings about a change in another part of the body.

• There are several hormones that are key to plant success:– Auxins– Gibberellins– Cytokinins– Abscisic Acid– Ethylene

Auxins• Auxins are plant hormones that cause cell

elongation. The result is a controlled growth direction in the plant.

• Auxins have opposite effects in different areas of the plants.– Shoots – Auxins move away from sun to bend

plant toward the sun.– Roots – Auxins move to the sun to bend plant

away from it.– Auxins can also respond to touch or solid

objects – the plant will grow around a large stone in the soil.

Gibberellins & Cytokinins• Gibberellins are plant hormones that have

several effects:– Work with auxins to promote elongation of

stems & roots.– Promote leaf growth.– Promote flowering.– Assist in germination.– Increase fruit production – agriculture uses this

to produce larger produce.• Cytokinins are plant hormones that

promote cell division and cell differentiation. They help some plants from aging to quickly and help keep them fresher for a longer time period.

Abscisic Acid & Ethylene• Abscisic acid (ABA) works to inhibit

growth of plants – not help it. It actually speeds up the fall of leaves and induces dormancy within the plant. This may aid in the plant preparing for the late Fall and Winter months.

• Ethylene is involved in the ripening of fruit.

• Carbon dioxide is used by industry to stop the effects of ethylene but it can not reverse them.

That’s All I Got…