Bellwork: What makes a plant a plant Bellwork: What makes a plant a plant? Describe the general life cycle of a plant

What is a plant? Section 22.1

What do plants need to survive? Plants form part of the kingdom Plantae Cell wall containing cellulose Photosynthesize using chlorophyll a and b Most are autotrophs, a few are parasites or saprobes Plants need Sunlight Required to carry out photosynthesis Plants needs to exchange gas Oxygen for cellular respiration Carbon dioxide for photosynthesis Issue is to exchange gasses and not loose too much water at the same time Plants need water and minerals Plants essentially sweat Plants have evolved to limit water loss and speed up uptake from the ground Minerals in the soil are needed for plant growth

How have plants adapted to life on land? It is thought that all land plants originated in the water Most photosynthetic organisms were unicellular eukaryotes, similar to today’s green algae Confused evolutionary biologists at first – how can algae and an oak tree be in the same kingdom? Cell walls and photosynthetic segments are the same! Have the same reproductive cycles Genomes are also closely related

The first land plants Fossil spores of land plants have been dated to 475 million years ago No actual plant fossils Oldest fossilized land plants are approximately 425 million years ago No leaves and roots, only a few cm tall Difficulty obtaining water Growed close to the ground in damp locations Plants evolved to be more resistant to the drying rays of the sun, capable of conserving water and reproducing without water Emergence changed land, changed ecosystems Many groups developed – mosses, ferns, cone bearing plants and flowering plants Adapted differently to a range of terrestrial environments

The plant kingdom Can be divided into five major groups based on four important features Embryo formation Specialized water conducting tissues Seeds Flowers

What defines most plant life cycles? The life cycle of land plants has two alternating phases – a diploid phase and a haploid phase Alternation of generations Sporophyte – multicellular diploid phase Gametophyte – multicellular haploid phase

Trends in plant evolution Gametophyte size has decreased and sporophyte size has increased Most green algae have a diploid sporophyte phase, some don’t Only multicellular bodies are gametophytes Ferns and their relatives have a small gametophyte and a larger sporophyte Seed plants have an even smaller gametophyte which is contained within sporophyte tissues.

Key point questions What do plants needs to survive? How did plants adapt to life on land? What features define most plant life cycles? How have plants in general changed over time?