Chapter 22 – Plant Diversity

What is a plant? Plants are multi-cellular eukaryotes that have cell walls made of cellulose They contain chlorophyll a and b Plants include trees, shrubs, grasses, mosses and ferns

The plant life cycle plants also have alternating generations A diploid (2N) phase and haploid (N) phase Diploid is known as the sporophyte, or the spore producing plant Haploid is known as the gametophyte, or the gamete- producing plant a gamete is a reproductive cell that is produced by mitosis and fuses during fertilization with another gamete to produce a new individual , the diploid sporophyte

Early Plants algae and photosynthetic prokaryotes added the oxygen to our planet’s atmosphere and provided food, animals, and microorganisms. origins in the water – the first plants evolved from an organism much like the multicellular green algae living today They also have reproductive cycles as well as cell walls and photosynthetic pigments that are identical to plants

What plants need to survive? The earliest type of plants were mosses and ferns Sunlight Water and minerals – in the soil that plants need to have to grow Gas exchange – require oxygen and carbon dioxide Movement of water and Nutrients – have specialized tissues that carry water and nutrients upwards from the soil

The First Plants it is thought that with DNA sequences and pigments that plants might have come from green algae The oldest fossil known to us nearly is are you reading what you are writing 450 million years old The fossils suggest that the first true plant were still dependent on water to complete their life cycles Over time, the demands changed and with evolution favoring plants that could survive without water

From water to land - What are some of the challenges?   challenge #1 - getting water and nutrients - in water, algae is bathed in nutrients and gets them by diffusion, water is brought in as needed by osmosis solution - roots and vascular tissue - roots take water and nutrients from the soil and transports them to the stem - some roots also act as food storage organs, beet root, sweet potato

- xylem transports water, phloem transports sugars - vascular tissue - tubes made of long cells that transport water and nutrients - xylem transports water, phloem transports sugars - more effective means of getting nutrients to all parts of the plant than diffusion and osmosis - Imperative as plants became more complex and larger

- the dry environment necessitated a mechanism for water conservation - challenge #2 - preventing water loss - the dry environment necessitated a mechanism for water conservation -  the solution - cuticles and stomata - land plants developed a waxy coating that prevents water loss, called a cuticle  - wax is a lipid, lipids are insoluble in water   

- stomata are openings in the leaves of plants that allow gasses to be exchanged during photosynthesis - guard cells fill with water in the day and open to allow carbon dioxide in and oxygen and some water vapor out - at night the guard cells lose water and close, this prevents even more water loss

challenge #3 – reproduction - in the water gametes are released and fertilization takes place, on land the gametes have to be protected from drying out until fertilization occurs - after fertilization the embryo has to be protected until conditions are good for growth and development

- What are the benefits of fruit? -    the solution - spores, seeds, and strategies for dispersal - spores - mosses and ferns produce spores that are dispersed by the wind, these plants still have to be in wet areas because the sperm must swim to the eggs - seeds - protects the embryo and provides food, some seeds are contained in fruit - What are the benefits of fruit? - Reproductive strategies - land plants adapt to the lack of water in many ways

challenge #4 - gravity, wind, and weather the solution - stems and roots - stems provide support for the plants and contain the vascular tissue - roots provide an anchor for plants

We divide plants into four different categories based on 3 features Water conducting tissue Seeds Flowers Through DNA and the project called Deep Green, we have found strong evidence that plants evolved from green algae in freshwater rather than from the sea