Plant GrowthObjectives1. Identify the parts of the plant that are responsible for growth2. Explain the mechanisms of plant growth3. Discuss the external and internal factors that affect plant

growthHomework: Using your notes from Friday’s lesson

and Today’s lesson, create a poster showing the life cycle of an angiosperm.

Plant Growth and Development

• Growth: Process of increasing in size

• Differentiation: Cells become specialized to perform a particular function.

Primary GrowthPlants continue to grow in height for their entire lives.

• Increase in height comes from apical meristems.– Regions of actively dividing

cells found at the tips of plants

– Buds, stems, roots

• Growth from apical meristems is called primary growth.

• Always increases the height, not the width, of a plant.

Secondary Growth

• Arises from the lateral meristems (cambium).– Areas of actively

dividing tissue in stems and roots.

• Increases the width of a plant.

Primary Growth• Increases length of root or shoot.• Cells divide by mitosis, increasing number of

cells.• Cells growth longer and then differentiate

into different cell types.– Ie: parenchyma, epidermal, vascular

• Shoot: Produces tissues that form stem, leaves and flower.

• Increase in plant height• Differentiation is determined by cell’s

location.– Ie: outer cells become epidermal cells

Root: Produces cells of root cap and other root cells.

Zone of cell divisionCells divide to create more cells.

Zone of elongationCells stop dividing and increase in length.

Zone of differentiationCells differentiate and tissues of root take on specialized functions.

Secondary Growth

• Arises from lateral meristems.

• Forms secondary tissue.

• Causes an increase in diameter or width of plant.

• Cambium produces secondary xylem and phloem.

• Every year vascular cambium produces new secondary xylem and phloem.

• Produces growth rings.

Check Point

1. Where are the apical meristems?

2. What results from their activity?

3. What is the difference between primary and secondary growth?

4. How would plants that exhibit secondary growth differ in size and structure from plants that exhibit only primary growth?

Homework..

Homework: Use you notes and text book to create a poster showing the life cycle of an angiosperm.

You must include diagrams showing: (Don’t copy the text book – You should include more detail…)– Reproductive parts– Pollination– Fertilization– Germination– A cycle starts and ends in the same place (p 398)• How would you fit what you learned today about

plant growth into this cycle?

Plant Growth – Part II

External and Internal Factors Affecting Plant Growth

Control of Plant Growth…

• What do plants require to grow?

• Some of the external factors affecting plant growth are…

• Light – Energy Source

• Food

• Water

• Temperature

• Soil pH

Light Requirements…

• Light is required for photosynthesis.

• Quantity is limited by environmental factors– Latitude and competition from other plants

• Quality is influenced by . . .– Shade from other plants– Cloud cover– Time of day– Seasons

Nutrient Requirements

• Create a table to – summarize the function of water, nitrogen,

potassium, calcium and magnesium and phosphorus in plant growth

– summarize some symptoms that plants may exhibit when they are deficient or lacking these nutrients.

• What role do you think water plays in helping plants absorb these nutrients?

Deficiency SymptomsNitrogen Deficiency Magnesium Deficiency

Phosphorous Deficiency

Internal Factors Affecting Plant Growth…

• Plant growth is influence by hormones just like our growth is influence by hormones…

Tropisms…• A directional change in growth or

movement in response to a stimulus…

• Controlled by plant growth regulators.– Chemicals produced by plant cells

that regulate growth and differentiation

• Phototropism: A change in direction of growth in response to light.

Gravitropism: A change in growth pattern in response to gravity.

Thigmotropism: A directional change in growth pattern in response to touch.

Heliotrope: A plant that turns,

throughout the day, so it is

facing the sun.

This is an example of what type of tropism?

Growth Regulators..

• They can stimulate or inhibit growth.

• There are five main hormone groups:

1.Auxins

2.Gibberellins

3.Cytokinins

4.Ethylene

5.Abscisic Acid

Find out what they do…(Student Activity)

Auxins

• Apical stem is main site of synthesis

• Primary role: promote cell elongation

• Also…

• Can inhibit cell division in some tissues.

• Stimulates cell division in vascular cambium.

• Helps regulate gravitropism.

• How auxin and phototropism causes the plant to grow in the direction of the sun.

• The auxin collects on the dark side of the shoot; therefore, more growth will occur on this side of the plant. The shoot will gradually lean towards the sun.

Gibberellins…

• Promotes cell division and elongation in plant shoots.

• Plays a role in flowering and fruit formation.

• Can be used commercially to stimulate seed germination.

Cytokinins…

• Promotes cell division and leaf mesophyll growth.

• Found in meristems, young leaves and growing seeds (actively dividing).

• Slow cell aging by inhibiting protein break down and stimulating protein synthesis.

Ethylene…

• A gas produced at various stages of development

• Causes changes that protect plant against environmental stress

• Ie stimulates plants to lose leaves in drought (prevent water loss)

• Regulates the growth of plant roots and shoots around obstacles

• Stimulates fruit ripening, root and shoot growth, cell differentiation, flower opening, leaf and fruit drop…

Abscisic Acid (ABA)…

• Primary role: Inhibit growth• Levels increase in response to seasonal

changes– Maintains dormancy in leaf buds and seeds– Dormant plants are less vulnerable to damage

• Controlling the closing of stomata in dry conditions.– Dry leaves wilt inducing the production of ABA

which diffuses into guard cells inducing them to close

Plenary…

1. Name the five growth regulators that are found in plants.

2. Which growth regulators promotes cell elongation? Cell elongation?

3. What problem would a plant have if it were deficient gibberellins? Why?

4. What is phototropism and how does it affect plant growth? What role does auxin play in this?

Homework…

Finish your assignment outline for tomorrow.

You will be marked out of 4 for completeness, organisation, collection of information, citing of sources.

Page 542 in your text

# 5 and 6