Origins of Plant Life and Plant Adaptations

Recall that algae are plant-like protists that are not classified as plants because they lack true roots, stems and leaves.

There are a number of striking similarities between plants and algae.

1. Eukaryotic2. Both possess chlorophyll. Chlorophyll is the pigment that

causes plants and algae to be green, and allows each of them to make their own food using photosynthesis.

Plants Have Similarities to Algae

3. Both plants and algae use starch as a storage product. Starch is many glucose (sugar) molecules bonded into a long chain.

4. Both plants and algae have cells walls that are composed of the strong, resistant material known as cellulose.

Plants Have Similarities to Algae

Main Idea:Plants Evolved from Green Algae

Genetic analysis has allowed scientists to determine that all species of plants like evolved from the same green algae ancestor.

This class of algae, Charophyceae, was the origination of several important plant characteristics:

- Multicellular body which led to specialization of structures and tissues

- Cell division method that allows new cells to communicate with each other chemically through holes in the cell wall

- Reproduction that involves sperm travelling to egg.

Plants Evolved from Green Algae

Recall the theory of natural selection: organisms that are best adapted to their environment will survive and will have the greatest opportunity to reproduce.

In the first charophyceans, the environment probably favoured those that could withstand longer dry periods.

As a result of this, eventually the first plant species evolved. True plants have multicellular embryos that remain attached to the female parent as they develop.

Natural Selection Played a Role

The Cactus: Good at Dry PlacesAdaptations of Cacti:1. Succulent tissue – able to

absorb moisture from the air through the dermal layer.

2. Leaves in the form of spines – protects against herbivores AND provides shade for the dermal layer, preventing water loss through evaporation.

3. Thick bodies that are spherical in form, which allows cacti to retain maximum amount of moisture by reducing exposed surface area.

Comparison of First Plants and Plants of Current Day & Age

First Plants Current Plants

Did not possess developed organs & systems for reproduction, relied on water droplets to transport sperm.

Possessed no vascular system to transport nutrients, so needed to stay close to water source.

Adapted for pollination by animals, wind, and other means.

Many possess vascular systems that allow them to transport nutrients to other parts of the plant, liberating them from water and allowing them to grow in drier areas.

1. Support their own weight2. Transport of sperm and spores3. Transportation of nutrients4. Preventing drying out

Challenges for Early Plants Living on Land

Plants who were the most suited to dealing with these challenges are the ones who got the most opportunity to reproduce, and this is how natural selection played a role in the development of particular organs and systems.

Plants require moisture in order to perform photosynthesis and stay alive. The following structures developed as a result of this necessity:

Cuticle – a waxy, waterproof layer that helps hold in moisture. The cuticle is particularly noticeable on leaves.

Stomata (stoma singular) – small holes in the cuticle that prevent water loss and allow air to move in and out.

Retaining Moisture

The Stomata: Useful Structures

Growing taller is an advantage to plants as they get more exposure to sunlight. It is also a problem, however, because plants also need nutrients from the soil.

In response to this challenge, a vascular system in plants was favoured by the environment.

A vascular system in plants allow water and mineral nutrients to travel up to the upper parts of the plant from the soil, and sugar from the leaves to travel down.

Transporting Resources

Xylem and Phloem Form Vascular System

Growing towards the sunlight is great for a plant, but if it can’t hold itself up at a particular height it will not get enough sun and will also be crushed under its own weight.

Lignin is a support material that hardens the cell walls of vascular tissues, and allows the plant to be strong enough to hold itself up.

Growing Upright

In plants, similar to humans, eggs are fertilized within the tissue of the parent. A fertilized egg develops into an embryo, the earliest stage of growth for a plant.

Some plants need free-standing water to transport sperm to the eggs of the female plant structures.

Pollen and seeds eliminate water as a necessity for plant reproduction.

Reproducing on Land

When the seed encounters conditions that are ideal for development (such as moisture), the embryo will develop into an adult plant.

Seeds

Pollen is a two-celled structure that contains a cell that will divide in two to form sperm. Pollen, as you have probably heard, can be carried by wind or animals to female reproductive structures.

A seed is a storage device for a plant embryo. Seeds contain a plant embryo along with a food supply to keep it alive.

Seeds are interesting in that they can remain dormant for many years if conditions for growth are unfavourable. As long as the seed has a food supply, the embryo can survive.

Pollen and Seeds

Mutualism is a form of interaction between two organisms in which they both benefit. Plants and certain animals have a mutualistic relationship when animals feed off the nectar of plants and hence transfer pollen to other plants.

Plant Evolution & Other Organisms