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Chapter Presentation

Transparencies Standardized Test Prep

Visual Concepts

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Plant Growth and DevelopmentChapter 26

Table of Contents

Section 1 How Plants Grow and Develop

Section 2 Regulating Growth and Development



Section 1 How Plants Grow and Develop

Objectives

• Compare seed germination in beans and corn.

• Contrast annuals, biennials, and perennials.

• Explain how primary and secondary growth are produced.

• Describe several traits of bread wheat.

• Contrast development in plants and animals.

Chapter 26



Seeds Sprout

• A seed contains a plant embryo that is in a state of suspended animation.

• A seed cannot sprout until water and oxygen penetrate the seed coat.

• If enough water and oxygen are available after the seed coat breaks, the young plant, or seedling, begins to grow.

Section 1 How Plants Grow and DevelopChapter 26



Seeds Sprout, continued

Germination

• A plant embryo resumes its growth in a process called germination.

• The first sign of germination is the emergence of the embryo’s root.

• After the shoot of a seedling emerges, its roots and shoots continue to grow throughout its life.




Seed Germination




Germination of a Monocot




Germination of a Dicot




Seeds Sprout, continued

Plant Life Spans

• A perennial is a plant that lives for several years. Most perennials reproduce many times during their life span.

• An annual is a plant that completes its life cycle (grows, flowers, and produces fruits and seeds) and then dies within one growing season. Virtually all annuals are herbaceous plants.

• A biennial is a flowering plant that takes two growing seasons to complete its life cycle.




Meristems

• Plants grow by producing new cells in regions of active cell division called meristems.

• Growth that increases the length or height of a plant is called primary growth.

• Growth that increases the width of stems and roots is called secondary growth.




Meristem




Meristems, continued

Primary Growth

• Apical meristems, which are located at the tips of stems and roots, produce primary growth through cell division.

• The new cells produced by apical meristems differentiate into the primary dermal, ground, and vascular tissues of roots, stems, and leaves.

• Some of the cells produced by the root apical meristem also become part of the root cap.




Apical Meristems




Primary Growth in Plants





Secondary Growth

• Secondary growth is produced by cell division in two meristems, which form thin cylinders near the outside of woody stems and roots.

• One meristem, called the cork cambium, lies within the bark and produces cork cells.

• The other meristem, called the vascular cambium, lies just under the bark and produces vascular tissues.





Secondary Growth

• A woody stem develops in three steps:

Step 1 A young woody stem has a ring of vascular bundles between the cortex and the pith.

Step 2 A vascular cambium forms between the xylem and phloem in each vascular bundle. Cork cambium forms under the epidermis.

Step 3 In a mature stem, the vascular cambium adds new layers of secondary xylem and phloem each year. The layers are called annual rings.




Development of a Woody Stem




Secondary Growth in Plants




Bread Wheat




Bread Wheat (cont.)




Plant Development

• Plants continuously make new cells in meristems. These cells differentiate and replace or add to existing tissues. Thus, a plant continues to develop throughout its life.

• Many cells in a mature plant can activate all of their genes. These cells can undergo differentiation and develop into a mature plant.

• A technique called tissue culture is used to grow new plants from tissue that can reverse its development.




Section 2 Regulating Growth and Development

Objectives

• Identify the major nutrients plants need to grow.

• Describe how plant hormones control plant growth.

• Relate environmental factors to plant growth.

Chapter 26



Nutrients

• Plants need only two raw materials—carbon dioxide and water—to make all the carbohydrates in their tissues.

• Like animals, plants also need oxygen for cellular respiration.

• Plants also require small amounts of at least 14 mineral nutrients, which are elements absorbed mainly as inorganic ions.

Section 2 Regulating Growth and DevelopmentChapter 26



Major Mineral Nutrients Required by Plants




Mineral Nutrients and Plants




Hormonal Control of Growth

• For centuries, people have known that plants bend strongly toward a light source as their shoots elongate.

• In the 1920s, the Dutch biologist Frits Went showed that a chemical produced in the shoot tip causes this bending response.

• Went named the growth-promoting chemical that causes stems to bend auxin.




Hormonal Control of Growth, continued

• The steps in Went’s experiment are:

Step 1 Went removed the tip of an oat shoot and placed the tip on an agar block.

Step 2 Went then transferred the agar block to the cut end of a shoot, which caused the shoot to grow.

Step 3 Went placed a block with auxin on one side of a shoot, and the shoot grew in the opposite direction.

Step 4 As a control, Went placed an agar block without auxin on the cut end of other shoots. These shoots did not grow.




The Steps in Went’s Experiment





Auxin

• Auxin is one of many plant hormones. A hormone is a chemical that is produced in one part of an organism and transported to another part, where it causes a response.

• Auxin causes plant cell walls to become more flexible, which allows the cells to elongate as they grow. Auxin accumulates on the dark side of a stem.

• Auxin also inhibits the growth of the buds along a stem. This inhibition is called apical dominance.




Auxins




Apical Dominance





Hormones in Agriculture

• Most plant tissues produce ethylene. Today, ethylene is used to promote the ripening of tomatoes, bananas, and other fruits that are harvested before they ripen.

• Gibberellins are produced in developing shoots and seeds. They stimulate stem elongation, fruit development, and seed germination.

• Cytokinins, which are produced in root tips, stimulate cell division and slow the aging of some plant organs.




Types of Plant Hormones




Ethylene




Cytokinins




Environmental Influences on Growth

Tropisms

• A tropism is a response in which a plant grows either toward or away from a stimulus.

• Phototropisms are responses to light. Responses to gravity are called gravitropisms. A thigmotropism is a response to touch.

• If a plant grows toward a stimulus, the response is called a positive tropism. If a plant grows away from the direction of the stimulus, the response is called a negative tropism.




Tropism




Gravitropism in Plants




Environmental Influences on Growth, continuedPhotoperiodism

• The response of a plant to the length of days and nights is called photoperiodism.

• A plant that responds when days become shorter than a certain number of hours is said to be a short-day plant.

• A plant that responds when days become longer than a certain number of hours is called a long-day plant.




Flowering and Photoperiodism




Photoperiodism




Environmental Influences on Growth, continuedResponses to Temperature

• Temperature affects growth and development in many plants.

• Many plants that flower in early spring will not produce flowers until they have been exposed to cold temperatures for a certain number of hours.

• Dormancy is the condition in which a plant or a seed remains inactive, even when conditions are suitable for growth.




Dormancy




Multiple Choice

The diagram below summarizes an experiment investigating the hormonal control of growth in an oat shoot. Use the diagram to answer questions 1–3.

Standardized Test PrepChapter 26



Multiple Choice, continued

1. What happened in step 2?

A. Auxin from the agar block stimulated the shoot to grow.

B. The shoot produced auxin in response to the agar block.

C. The agar block stopped further growth of the shoot.

D. The shoot grew straight up in response to an agar block.






A. Auxin from the agar block stimulated the shoot to grow.

B. The shoot produced auxin in response to the agar block.

C. The agar block stopped further growth of the shoot.

D. The shoot grew straight up in response to an agar block.






F. The weight of the agar block caused the shoot to bend.G. Exposing one side of the shoot to auxin caused

the shoot to grow in the opposite direction.H. The agar block shielded one side of the shoot from light, causing the shoot to grow in the opposite direction.J. Auxin from the agar block caused the shoot to exhibit positive gravitropism.






F. The weight of the agar block caused the shoot to bend.G. Exposing one side of the shoot to auxin caused

the shoot to grow in the opposite direction.H. The agar block shielded one side of the shoot

from light, causing the shoot to grow in the opposite direction.J. Auxin from the agar block caused the shoot to exhibit positive gravitropism.





3. What would likely happen if an agar block without auxin were placed on the cut end of an oat shoot?

A. The shoot would grow straight up.

B. The shoot would grow straight down.

C. The shoot would bend and grow around the agar block.

D. The shoot would not grow.





3. What would likely happen if an agar block without auxin were placed on the cut end of an oat shoot?

A. The shoot would grow straight up.

B. The shoot would grow straight down.

C. The shoot would bend and grow around the agar block.

D. The shoot would not grow.


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