Plants

Plants evolved about 500 million years ago from simple green algae that lived in the ocean. All plants are autotrophic and some, like the famous Venus fly-trap, can also be heterotrophic. All plants are eukaryotic and multicellular. Their cells contain a nucleus and membrane bound organelles, specifically chloroplasts. In addition, plant cells also contain a cell wall composed of cellulose. The cell wall provides protection, structural support and helps to regulate water pressure within the plant cell.

The diagram on the right illustrates the components of a plant cell. You will notice the presence of vacuoles which help to store the materials needed for photosynthesis. Animal cells and plant cells contain most of the same organelles, but it is important that you note the differences.

Currently there are over 350 000 species of plants. They include mosses, ferns, conifers and flowering plants. Most plants live on land and can withstand a wide variety of climates. Cacti live in arid, dry areas whereas mosses need to be in moist environments to survive.

Evolution of Plants The transition from a mainly aquatic environment to a terrestrial planet revolved around plants. The ability of plants to photosynthesize and sustain themselves is a key factor in the evolutionary process. Plants provided nutrition to other organisms and they helped form soil. Taller trees helped to reduce temperatures by providing shade and therefore promoted the growth of other organisms previously affected by hot and dry conditions. Trees and shrubs also provided habitats for many other organisms.

Plants evolved during this process. Surviving in an aquatic environment is much different than living in a terrestrial environment. In water, plants were constantly provided with water and minerals and were able to easily release waste products. However, on land plants had to either live in moist environments or develop a method that allowed them to absorb and transport materials within their cells. They would have to develop specialized cells to carry out tasks and provide structural support. So, of course plants evolved too.

Classification Plants are classified based on the presence or absence of vascular tissue. Vascular tissue can be compared to arteries and veins. It is a network of specialized cells that allows plants to transport water, minerals and sugar throughout the plant. You will learn about the characteristics of nonvascular plants and vascular plants.

A quick word from Hank https://www.youtube.com/watch?v=iWaX97p6y9U&list=PL3EED4C1D684D3ADF&index=36

Nonvascular Plants Mosses, liverworts and hornworts are examples of bryophytes. Bryophytes are nonvascular plants that lack specialized transportation cells called xylem and phloem. In addition, they do not have distinct roots, stems or leaves. As long as the environment is moist they can grow on soil, dead trees, rocks and even buildings. However, they cannot grow very tall.

Reproduction of Nonvascular Plants Bryophytes can reproduce asexually through vegetative reproduction. This occurs when a part of the plant breaks off and a new identical plant develops. To reproduce sexually, these plants require water for the male reproductive cell to swim to the female reproductive organ. Unlike animal cells that produce haploid sex cells to produce a zygote, plant cells alternate the type of cells they produce. In one generation, a plant produces haploid cells called spores which develop into a haploid plant.

The haploid plant, called a gametophyte, produces and releases haploid gametes. When two of these gametes fuse together, a zygote forms. The zygote, which is diploid, develops into a sporophyte plant. The sporophyte plant then releases haploid spores and the cycle continues. The image on the right shows two capsules that contain many spores. Each of the spores can develop into a new plant. Moss reproduction

Homework Watch the two videos: https://www.youtube.com/watch?v=iWaX97p6y9U&list=PL3EED4C1D684D3ADF&index=36 Moss reproduction And can you bring in a device that is capable of reading a pdf tomorrow please.