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UMass Amherst BIOLOGY 152 - Meeting Multicellular Challenges --Plants

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Lecture 7 Outline of Last Lecture i. Hox Genes ii. 2R hypothesis iii.Pax-6 Genes b. Combinatorial i. Floral Morphology ii. ABC hypothesis Outline of Current Lecture II. Plant Structure a. Adapting to Dry Land b. Shoots and Leaves i. Anatomy of A Leaf Current Lecture Meeting Multicellular Challenges — Plants Challenges that a multicellular organism (in this case a plant) must overcome •limits of diffusion/distribution •cell adhesion •regulation of cell fate and division Plant Structure Adapting to Dry Land •non-vascular plants —> vascular —> flowering •in non-land plants: •didn’t have to support themselves —water acted like a skeleton holding them up Bio 152 1!!!These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best !used as a supplement to your own notes, not as a substitute. !!•aquatic sperm — had sperm that would swim between plants •they didn’t need roots, didn’t get nutrition from soil, they got it from water •didn’t need to worry about desiccation (drying out) •non-vascular land plants limited in size because they must get water to all of their cells Innovations that allowed these plants to live on land: •waxy cuticle — waxy coating on the outside of the plant to prevent water loss •helps with diffusion, distribution, defense •vasculature — tubes •helps with diffusion, cell adhesion/support, and cell to cell communication •stomata — “little mouths” on leaves of plant to let water in and CO2 out •essential in diffusion •seeds •help regulate cell division and cell fate (development and reproduction) and defense **Clicker Question** Have non vascular plants been entirely displaced by vascular ones? NO **Clicker Question** Did plants evolve vasculature before or after moving onto land? AFTER •there are nonvascular land plants that exist •land plants evolved early on without vasculature **Important note: this is different than what we learned previously about how a trait had to already be in existence for the organism to evolve. That is because the difference lies in what makes the vasculature in plants Shoots and Leaves Basics of the herbaceous plant body!•Shoot •reproductive organs (stamen, carpel) •leaf •stem •roots Anatomy of a Leaf: •dermal tissues — protect plant from water loss (desiccation) •ground tissues — internal tissue, the part that photosynthesizes (anything not outside or the vasculature) •vascular tissues — pholem and xylem, transport water and sugar and are the “veins” seen in the leaves **Clicker Question** Mesophyll cells in the leaf photosynthesize (transduce light into the production of sugars). Of the following, which raw materials are needed to do this? O2, CO2, H2O, carbohydrates •CO2 — it is the raw material responsible for making C-C bonds in sugars •water !The cells in the middle of the leaf need CO2, however there is a waxy cuticle surrounding the leaf that while keeping water in, also keeps CO2 out. So how does the CO2 get inside? •stomates (“little mouths”) •surrounded by 2 cells called guard cells !This picture shows a guard cell closed (left) and a guard cell open (right) — understanding how these work is one of the key ways to understanding how plants work!!**Clicker Question** Plants, like fungi, have cell walls (animals don’t). These walls are made of cellulose. The cellulose can be digested away using enzymes to create a protoplast. It is possible to protoplasts with guard cells. How could a stomate be opened or closed (needs to be readily reversible)? • influx of water, allows for quick changes •although ATP synthesis would be happening, it is not responsible for the action of the stomates Which state would be an open stoma? • The right one •the cell wall is rigid (has cellulose microfibrils wrapped around — when water comes in it causes swelling and forces them apart •they open when lots of water is around, and close when there isn’t much water present •looking at the picture, if the water comes in, the cell swells and pushes against the wall (the cells on the right side are swollen with water) How does a cell do this? Example: take a beaker and put a membrane down the middle of it, that is permeable to potassium (K). Over time it will equilibrate — the same concentration of K will be on both sides of the membrane. So if the membrane isn’t permeable for the solute, and the concentration of solute was higher on the left, then water would move to the left side of the membrane to equate the water and solute concentration on both sides of the membrane. **Clicker Question** How can the plant cause the stomate to open? •pump solutes into the cytosol!•increase the internal sugar concentration •plants use a combination of these two in order to open them up — in the morning they use ATP to pump K in, and in the evening they pump solutes out, water follows and in the absence of water the stomates close •this procedure is standard for a plant living in an environment where they get plenty of water In general plants draw a lot of water into their cells, they have a low water potential so water likes to flow into them. •water —> plant cells —> membrane swells —>creates structural support •when you fail to water a plant (such as a tobacco plant seen in the slides), they’re not able to maintain a 3 dimensional structure, because in order **Clicker Question** When should stomates be open? •in a plant adapted to live in a temperate environment they should be open during the day •if a plant lives somewhere without a lot of rainfall it opens its stomates at night and closes them during the day to prevent desiccation •these plants have developed a different photosynthetic mechanism because otherwise they would need to have stomates open during the day to get CO2 **Clicker Question** Apply concepts to animal cells Red blood cells (erythrocytes) carry oxygen around in the blood plasma which is roughly 300 mM. The higher this number, the more osmotic molecules in the solution. What actions might lead to the erythrocytes looking more “spherical”? •if you added distilled water to test tube, the 300 mM will go down, and the water will go into the cell •you can add distilled water to the test tube •you can also add water with 100 mM to tube •would both give you spherical looking cells because solute conc. inside cell would still be


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