TOPIC 9.3 GROWTH IN PLANTS

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1 TOPIC 9.3 GROWTH IN PLANTS

2 9.3 A Growth

3 INTRO IB BIO In general, plants are able to grow indeterminately. This means they are not restricted to being a certain size or reaching a certain stage of maturity.

4 INTRO IB BIO Unlike most animals, plant plant cells (even differentiated) are able to generate whole new plants. These cells are totipotent and have the ability to fully differentiate into any plant tissue.

5 IB BIO Understandings Growth in plants is restricted to regions known as meristems. U1: Undifferentiated cells in the meristems of plants allow indeterminate growth. These areas are composed of undifferentiated cells that undergo cell division and allow indeterminate growth. Primary meristems are found at the tips of stems and roots and are called apical meristems. Meristem Apical Meristem

6 IB BIO 9.3 There are two main types of 6 Understandings U1: Undifferentiated cells in the meristems of plants allow indeterminate growth. meristems that are found in plants: Root apical meristems are responsible for growth of the root. Shoot apical meristems are located at the tip of the stem. Meristem Apical Meristem Cells in meristems undergo the cell cycle repeatedly to produce new cells. This increases plant volume/mass.

7 IB BIO Understandings U2: Mitosis and cell division in the shoot apex provide cells needed for extension of the stem and development of leaves. The shoot apical meristem throws out cells that are needed for growth of the stem. It also produces groups of cells that grow and develop into leaves and flowers. Meristem Apical Meristem Every time a meristem cell divides, one cell remains while the other differentiates and develops.

8 IB BIO Understandings U2: Mitosis and cell division in the shoot apex provide cells needed for extension of the stem and development of leaves. Each apical meristem can give rise to additional meristems that can differentiate into different tissues. Chemical signals determine which type of specialized tissue develops from the undifferentiated cells. Meristem Apical Meristem

9 IB BIO Understandings U2: Mitosis and cell division in the shoot apex provide cells needed for extension of the stem and development of leaves. Young leaves are produced at the sides of shoot apical meristems. They appear as small bumps called leaf primordia. Meristem Apical Meristem

10 VIDEOS IB BIO 9.3 Plant Time Lapse 10 Difference Between Apical/Lateral Meristems FuseSchool: Plant Growth

11 9.3 B Hormones & Tropism

12 IB BIO Understandings U3: Plant hormones control growth in the shoot apex. Hormones are chemical messages that are produced in one part of an organism that has an effect in another part. In plants, hormones control growth in the shoot apex (tip).

13 IB BIO 9.3 Auxins are a type of hormone that have many functions. For 13 Understandings U3: Plant hormones control growth in the shoot apex. example, they can trigger root growth, influence fruit development and regulate leaf development. Auxin

14 IB BIO Understandings U3: Plant hormones control growth in the shoot apex. As shoot apical meristems grow and form leaves, regions of meristem are left behind in the node. High auxin concentrations in these areas inhibit growth. The further a node is from the shoot apical meristem, the lower the auxin concentration. The ration of hormones determines whether auxillary buds will develop.

15 IB BIO 9.3 Understandings U4: Plant shoots respond to the environment by tropisms. Plants use hormones to control the growth of stems and roots. The direction that stems/roots can be influenced by external stimuli. Directional growth is called tropism and can include: Phototropism 15 Tropism Photropism/ Gravitropism Growth towards a light source Gravitropism Growth in response to gravitational forces.

16 IB BIO Understandings U6: Auxin influences cell growth rates by changing the pattern of gene expression. In phototropism, light is absorbed by photoreceptors called phototropins. When activated, they alter the gene expression to produce proteins pumps that transport auxin from cell to cell. Auxin

17 IB BIO Understandings U5: Auxin efflux pumps can set up concentration gradients of auxin in plant tissue. When plants detect the direction of a light source, effux pumps transport auxin to the more shaded opposite side of the stem. This concentration gradient triggers in growth on that side. Auxin This results in the stem growing towards the light. Leaves attached to the stem therefore receive more light and the rate of photosynthesis increases.

18 IB BIO Understandings U5: Auxin efflux pumps can set up concentration gradients of auxin in plant tissue. In gravitropism, stems grow in the opposite direction of gravity and while roots grow in the same direction. Auxin accumulates at the bottom of cells, resulting in faster growth upwards than downward. Auxin

19 VIDEOS IB BIO 9.3 Phototropism Timelapse 19 Plant Hormones FuseSchool: Plant Hormones

20 9.3 C Propagation

21 IB BIO Applications A1: Micropropagation of plants using tissue from the shoot apex, nutrient agar gels and growth hormones. Micropropagation is a technique used to produce large numbers of identical plants in vitro. In this process, a plant is identified that has some desirable feature. Micropropagation

22 IB BIO Applications A1: Micropropagation of plants using tissue from the shoot apex, nutrient agar gels and growth hormones. Tissues from the plant are sterilized and cut into small pieces. These samples are typically taken from shoot apical meristems as they contain the least amount of differentiated cells. Micropropagation

23 IB BIO Applications A1: Micropropagation of plants using tissue from the shoot apex, nutrient agar gels and growth hormones. Micropropagation The samples are then placed in nutrient agar gels containing plant hormones. If the ratio of hormones is correct (including auxin), the plant will develop and roots will form. These clones can then be planted and grown.

24 IB BIO Applications A1: Micropropagation of plants using tissue from the shoot apex, nutrient agar gels and growth hormones. Micropropagation

25 IB BIO Applications A2: Use of propagation for rapid bulking up of new varieties, production of virus-free strains of existing varieties and propagation of orchids and other rare species. Micropropagation can be used to produce virus-free plants. Since meristems are free of viruses, clones grown from meristem cells are not infected with a given virus. Micropropagation

26 IB BIO Applications A2: Use of propagation for rapid bulking up of new varieties, production of virus-free strains of existing varieties and propagation of orchids and other rare species. The technique can also be used to: Produce large quantities of plants with a desirable characteristic. The process takes up less space and is faster than normal production. Preserve rare species, such as orchids. Micropropagation The bulk production allows for wild replanting and commercial production.

27 IB BIO Applications A2: Use of propagation for rapid bulking up of new varieties, production of virus-free strains of existing varieties and propagation of orchids and other rare species. Resulting plantlets can also be frozen and stored via cryopreservation. This acts as a sort of seed bank and can protect species from extinction as a result of habitat loss. Micropropagation

28 VIDEOS IB BIO 9.3 Plant Tissue Culture: Micropropagation 28 Plant Tissue Culture in 3 Minutes

29 REVIEW IB BIO Define apical meristem. 2. Compare and contrast the role of the root and shoot apical meristems. 3. Define tropism. 4. Discuss the role of hormones in plant growth, using phototropism as an example. 5. Outline the process and potential applications of micropropagation.