Botany

KEY CONCEPTS

I. Plant Parts

II. Plant Processes

1. Photosynthesis
2. Respiration and transpiration
3. Sexual Reproduction
   1. Self-fruitful plants
   2. Self-sterile plants

III. Environmental Factors

IV. Groupings of Plants

II. PLANT PROCESSES

The three major processes that are the basis for plant growth are photosynthesis, transpiration, and respiration. All life on our planet depends on the first process, photosynthesis.

PHOTOSYNTHESIS

Photosynthesis is the process by which light energy is utilized to convert carbon dioxide and water into food to be used by plants. Oxygen is released into the air during the process. Light or solar energy is captured by chlorophyll (CHLOR-oh-phil), the green pigment in leaves. It is then converted into chemical energy which is stored as starch or sugar. These starches and sugars are stored in roots, stems and fruits. They are available to the plant as food or fuel.

Plants differ from animals in that animals cannot manufacture their own food from light energy. The word photosynthesis means "to put together with light."

6CO₂ + 6H₂O + energy 6 C₆H₁₂O₆ (glucose) + 6O₂

Photosynthesis depends on light. Plants vary widely in their requirement for light. Plants should be spaced in the garden so they receive the necessary amount of sunlight. Tall plants should not shade shorter plants. Trees may require pruning to ensure that adequate light reaches grass, flowers or shrubs planted nearby. 

RESPIRATION AND TRANSPIRATION

The food that a plant stores is used by the plant for new growth. The process of converting stored food into usable energy is called respiration. It is similar to burning wood to release stored energy as heat and light. Just as fire requires oxygen to burn, respiration, or the "breaking down" of stored sugars, requires oxygen to release energy for new growth.

Water and carbon dioxide are released during plant respiration. This is the same as in animal respiration. It occurs in all cells of a plant, in light or darkness. Respiration is essentially the opposite of photosynthesis. It uses food plus oxygen to change chemical energy into heat and an energy form usable by the plant. Light is not needed in this process. An example of a plant using stored food can be seen when a potato sprouts in storage.

C₆H₁₂O₆ + 6O₂ 6 6 CO₂ + 6H₂O + energy

Transpiration is a plant process that involves the movement of water through the plant. The loss of water through the leaf stomata pulls water up through the plant from the roots. Transpiration is the way plants use water to carry nutrients through their structure. When additional water is unavailable to the roots, as in winter or drought, wilting and potential plant damage can occur.

SEXUAL REPRODUCTION - HOW FLOWERS FORM SEED

Seed formation begins when the pollen is moved from the male part of the flower (the stamen) to the female part (the pistil). Pollination is the transport of pollen from the anther onto the stigma. Pollen can be carried by insects, other animals or wind.

When pollen touches the stigma, a long tube (the pollen tube) grows from the pollen down through the style until it reaches the ovary. Sperm (male sex cells) are released from the pollen tube and unite with eggs contained in the ovary. This union of egg and sperm is called fertilization. Fertilization results in an embryo which develops inside protective layers of tissue. The embryo and protective layers are called a seed.

The fragrance, nectar and color of flowers attract insects, birds and mammals. They carry pollen to the stigma resulting in pollination. Flowers lacking showy petals, as in many deciduous trees, are usually pollinated by the wind. The structure of the flower often gives clues about the mechanism for pollination.

SELF-FRUITFUL PLANTS

Self-fruitful plants may be pollinated with pollen from the same flower or other flowers on the same plant. Most plants are self-fruitful.

SELF-STERILE PLANTS

Some plants are self-sterile and cannot be fertilized by their own pollen. Pears, plums and some apples are self-sterile. They require the presence of another variety of apple tree, a "pollinator," for fertilization.

Cross-pollination is the carrying of pollen from one plant to another. Cross-pollination increases genetic variability. Genetic variability means that offspring plants carry the genetic information that may show new physical characteristics not seen in the parent plant. New color, shape, size, disease resistance and other plant characteristics may result. Plant breeders who search for new and better plants may use cross-pollination as one technique in their work.

When there are problems with lack of fruit, remember that some plants have incomplete flowers (one sex only) and may be dioecious (having only male or female flowers). They therefore require both a male and a female plant for seed formation. Lack of fruit also can come from flowers being self-sterile. Knowing that some plants are unable to set seed or fruit without a pollinator and what can be done to correct this are common home gardener issues.