Plant ProcessesChapter 12

M.ElizabethMLK JHS

2005-2006

Review

• What are the two types of reproduction?• What is the name of the plant female

reproductive organ?• What is the name of the plant male

reproductive organ?• What is the purpose of reproduction?• What are the two gases involved in

photosynthesis?• Where does photosynthesis occur in a plant

cell?• What is the name of the pigment which absorbs

light energy?

12.1 The Reproduction of Flowering Plants

• How does fertilization occur– Sperm cells produced in the stamen

must be able to reach eggs in the pistil.– Sperm cells within pollen grains move

down the pollen tube which the plant has produced, and into the ovary.

– Fertilization occurs when a sperm cell fuses with an egg cell.

A seed is born

Flower Anatomy

From Flower to Fruit

• After fertilization the following takes place:– the fertilized egg within the ovule

develops into a seed. – The ovary surrounding the ovule develops

into a fruit. – The fruit swells and ripens while holding

and protecting the developing seeds.– The seeds represent the next generation

once germinated and looking like a plant.

Seeds Become New Plants

• Once a seed is fully developed, the seeds stop developing and become DORMANT.– When seeds are dormant they are inactive

and the seeds metabolism stops.– Dormant seeds can survive long periods of

drought or freezing temperature.

• Once a seed is in an environment with water, oxygen, and a suitable temperature (ideally about 27C or 80.6F) the seed germinates or sprouts.

Andrew Syredhttp://www.visions-of-science.co.uk/winners2004/win-04.htm.

Seed Germination

Asexual Reproduction

• Parts of a plant are used to create a new plant without forming flowers or seeds;

• Examples:– Strawberry runners– Potato Tubers– Geranium slips

Don’t eat green potatoes.Potatoes belong to the nightshade family, and most green portions of plants in this family contain an alkaloid poison called solanine.

12.2 The Ins and Outs of Making Food

• Photosynthesis – light to sugar– Occurs in plant cell chloroplasts– Chloroplast contain chlorophyll, a green

pigment that absorbs light energy.– Chlorophyll is green because in the light

spectrum green is not absorbed, it is reflected.– The overall reaction involves multiple steps:

6 CO2 + 6 H2O C6H12O6 + 6O2

Gas exchanges occurs through leaf stomata (stoma, singular). Transpiration is the movement of water through the stoma.

What are the two gasses involved in photosynthesis?

12.3 Plant Responses to the Environment

• Response to Stimuli– Anything that causes a reaction in an

organism, organ system, organ, tissue, or cell is a stimulus.

• Tropism - Plants growth in respond to a stimulus either:– positively/towards the stimulus or – negatively/away from the stimulus:

Tropic Responses

– Light = phototropism •Stems are positively phototropic

–moving towards the light stimulus•Roots are negatively phototropic

–moving away from the light stimulus

– Gravity = gravitropism •Stems are negatively gravitropic •roots are positively gravitropic.

Current ideas about Phototrophism

• Cells produce a hormone called an auxin, indole-3-acetic acid (IAA) while growing

• Unequal distribution of auxin causes the bending in phototropism by affecting the cell length of plant cells– High concentration the cells become

longer – Low concentrations the cells become

shorter

Phototropic Effect

Adaptive Value of Phototropisms

• Roots growing down and/or away from light are more likely to find the soil, water, and minerals they need.

• Stems growing up and toward the light will be able to expose their leaves so that photosynthesis can occur.

What is the adaptive value of gravitropism?

• Think – Pair – Share

Seasonal ResponsesLength of Day

• The length of day changes over a season.

• Days are longer in the summer than in the winter.

• The difference between day and night length is an important stimulus for many plants.

• Length of day is a stimulus that determines when some plants will reproduce.

Poinsettia

Seasonal Changes in Leaves

• All trees lose their leaves• Evergreens and Deciduous Trees

– Evergreen trees shed their needle leaves a little at a time

– Deciduous trees lose their leaves at the same time each year.•Usually in the fall and winter •Tropics or areas near the Equator have

only wet and dry seasons so the deciduous trees shed leaves before the dry season begins.

Prickly Pear Cactus

• Desert plants live with extremes in temperature, water availability and solar radiation by adapting physically rather than behaviorally.

• Most desert plant adaptations seem to be geared towards minimizing water loss; a difficult task since plants must "breathe" in order to photosynthesize, losing body water to the atmosphere in the process..

Different Desert Adaptations:

• In their effort to survive in a hostile environment, desert plants have three adaptations types that have developed.

• Morphological - related to the form and structure of the plant

• Physiological - related to the biological function of the plant. Such features may include:· Accumulate water· Self-pruning· Plant chemically shifts temperature

• Behavioral - where the plant can surviveRemember plants cannot move· Grow where there is more water· Cracks in the sandstone - where water accumulates

Morphological features

• Fuzzy or hairy leaf surface• Waxy leaves• Shiny, reflective leaves• Small leaves• Deep tap roots• Extensive surface roots• Thicker leaves• Leaf orientation such that minimizes the area

exposed to midday heat• Spines instead of leaves• Thicker leaves• Grow in shade or self-shade

12.4 Plant Growth

• All living things grow. A plant’s growth is affected by its

• Genes: sequences of DNA that code for a particular trait. Heredity the passing of traits from one generation to the next.

• Hormones: are chemical messengers that carry information from one part of an organism to another, produced in small quantities when genes are expressed.

• Environment: determines behavior and appearance.

Plant Hormones

• A plant hormone is produced in a part of a plant, then moves through the plant to cause a response in all parts of the plant it contacts.

• Five classes of have been identified: 1. Auxin – growth stimulator, 2. Cytokinin – growth stimulator 3. Gibberellin – growth stimulator 4. Abscisic acid – growth inhibitor, promote

dormancy, and help the plant withstand stressful conditions.

5. Ethylene - growth inhibitors or "aging stimulators". A gas produced and involved in fruit ripening.

How Hormones Work

• Generally they work by affecting cell division, elongation and differentiation (telling the cell what DNA sequences should be expressed).

• Effects of the chemicals vary depending on target area, developmental stage, hormone concentration, and interactions with other hormones.

• At the cellular level, the hormones result in gene expression, effects on enzymes, or modifications of cell membrane properties.

Review

1. Which of the following statements is NOT true of flowering plants?a. Fertilization takes place within the

flower.b. They produce seeds in fruit.c. They use flowers to reproduce

asexually.d. They are the largest group of plants

in the world.2. Flowers can have both male and female

reproductive structures. True or False?

Review

3. The ovule becomes a _____________after fertilization.

4. A fruit, which protects and holds the seeds, develops from the __________ of a flower.

5. Green light is reflected by chlorophyll. True or False?

6.During photosynthesis, light energy is used to split water into __________ and ____________

7. Sugar is broken down by plant cells for energy during cellular respiration. True or False?

Review

8. Transpiration is the loss of water vapor from leaves. True or False?

9. When a tropism is _________, a plant will grow toward the stimulus. (positive or negative)

10. A plant’s traits are determined by heredity. True or False?

11. After seeds develop fully, and before they sprout, they may become ______________. (deciduous or dormant)

Review

12. During________________, energy from sunlight is used to make sugar. (photosynthesis or phototropism)

13. The loss of water through stomata is called _______________.(transpiration or tropism)

14. A change in plant growth in response to the direction of light is called_______________. (gravitropism or phototropism)

15. Plants that have leaves year-round are ______________. (deciduous or evergreen)

Review

16. Plants that seasonally lose their leaves are _____________.(deciduous or evergreen)

17. Plant cells need carbon dioxide for a. cellular respiration. b. phototropism. c. fertilization. d. photosynthesis.

18. When chlorophyll breaks down,a. pollination occurs. b. other pigments become visible.c. red pigments disappear. d. photosynthesis occurs.

Phototropism

• Early in the history of science, Darwin kept birds. To provide the birds with vitamins in those days, one needed to grow sprouts. A common species was Phalaris or canary grass!

• Darwin noted that the first leaf (coleoptile) of canary grass was very sensitive and responsive to light. He sprouted the seeds in flats and fed the mature seedlings to the birds. But before they made green leaves, the white first leaf (coleoptile) appeared and grew toward the light coming from the nearby window.

• Darwin was very curious about this and did a few experiments.