Plant Growth Objectives Identify the parts of the plant that are responsible for growth Explain the mechanisms of plant growth Discuss the external and internal factors that affect plant growth Homework: Using your notes from Friday’s lesson and Today’s lesson, create a poster showing the life cycle of an angiosperm.
Reproduction review What is one key difference between sexual and asexual reproduction? What is a major cost of asexual reproduction? How do humans use asexual plant reproduction? What are the functions of a seed? Why is it useful for a plant to disperse its seeds? What are two differences between gymnosperm and angiosperm reproduction? Is pollination the same as fertilization? What is the purpose of a fruit? What are some examples?
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.
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. • i.e. parenchyma, epidermal, vascular
Primary growth (cont’d) • 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
Primary Growth (cont’d) Root: Produces cells of root cap and other root cells. Zone of cell division Cells divide to create more cells. Zone of elongation Cells stop dividing and increase in length. Zone of differentiation Cells differentiate and tissues of root take on specialized functions.
Secondary Growth • Arises from the lateral meristems (cambium). • Areas of actively dividing tissue in stems and roots. • Increases the width of a plant. • Every year vascular cambium produces new secondary xylem and phloem. • Produces growth rings.
Arises from lateral meristems. Forms secondary tissue. Causes an increase in diameter or width of plant. Cambium produces secondary xylem and phloem. Secondary Growth
Check Point • Where are the apical meristems? • What results from their activity? • What is the difference between primary and secondary growth? • How would plants that exhibit secondary growth differ in size and structure from plants that exhibit only primary growth? • Would you be able to draw the life cycle of an angiosperm or gymnosperm fitting in primary and secondary growth?
Plant Growth – Part II External and Internal Factors Affecting Plant Growth
External 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 Homework - Create a table to 1. summarize the function of nitrogen, potassium, phosphorus, calcium and magnesium 2. 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?
Internal Factors Affecting Plant Growth… • Plant growth is influenced by hormones (plant growth regulators) just like our growth is influenced by hormones…
Growth Regulators.. • They can stimulate orinhibit growth. • There are five main groups: • Auxins • Gibberellins • Cytokinins • Ethylene • Abscisic Acid Find out what they do…(Student Activity)
Auxins • Synthesized in the shoot apical meristem • Promote cell elongation (key function) • Auxins can also: - inhibit cell division in some tissues (apical dominance) - stimulate cell division in vascular cambium - help regulate gravitropism (change in direction of growth due to gravity) Use of auxins – Herbicides with auxins promote unsustainable plant growth • Commercial fruit growers – induce cell elongation in fruits – ripen at the same time (less harvesting costs) • Removing apical buds to have more flowers, fruits or leaves
Gibberellins… Function: • Promote cell division and elongation in plant shoots; and cell differentiation • Play a role in flowering and fruit formation in many species • Help make carbos for embryo Commercial use: • gibberellin sprays used to stimulate fruit production (e.g. grapes) • Used by seed producers to stimulate seed production
Cytokinins… Function: • Promotes cell division; found in meristems, young leaves and growing seeds • Slow cell aging by inhibiting protein break down and stimulating protein synthesis Plant growth is a balance between the actions of auxins and cytokinins Commercial use: Cytokinin sprays for lettuce and mushrooms to keep them from rotting
Ethylene… • A gas produced at various stages of development Functions • Called the plant stress hormone because it causes changes that protect plant against environmental stress • - i.e. stimulates plants to lose leaves in drought (prevent water loss) or reduced yields in response to pollution (ozone) • 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, flower and leaf senescence
Abscisic Acid (ABA)… Function: • inhibits growth in response to changes in temperature and light (e.g. seasons) • Maintains dormancy in leaf buds and seeds • Dormant plants are less vulnerable to damage • Controls the closing of stomata in dry conditions • Dry leaves wilt inducing the production of ABA which diffuses into guard cells inducing them to close Commercial uses: ABA is sometimes applied to plants before they are shipped to enter dormancy, then gibberellins are sprayed
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.