Plant Organs and Organ Systems Plant Organs Roots

Plant Organs and Organ Systems

Plant Organs • Roots – Anchor the plant in the soil, which allows the plant to grow vertically. – Collect water from the surrounding soil and transport it to the stem. – Stores food that is made in other parts of the plant.

• Leaf – Main function is to support photosynthesis in the mesophyll (turning carbon dioxide and water into sugar and oxygen) – Xylem carries water and minerals needed from the root to the leaf, and phloem carries sugar to the rest of the plant or to the root for storage. – CO 2, and excess H 2 O enter and/or exit through openings called stomata, which are controlled by guard cells.

• Stem – Transports water and nutrients throughout the plant – Supports the leaves and flowers – Epidermis provides a protective covering and allows for gases and water vapour to enter/leave the cell. – Most plants have a cuticle (waxy substance) on the stem to protect the stem and to reduce water loss.

• Flower – The reproductive structure of the plant. – The flower contains male (stamens) and female (pistil) sex organs. – Each stamen consists of a filament with an anther at the tip, which produces pollen. – The pistil consists of the stigma, style, and ovary (where the eggs are located). – When the pollen and an egg unite, the fertilized eggs become a seed. – Some seeds are surrounded by a flesh (the fruit) which others have a hard shell.

Plant Organ Systems • A plant has two organ systems: – the shoot system – everything above the ground (the stem, leaves, buds, flowers, and fruits) – the root system – everything below the ground • These two systems and the organs within them are interdependent, just as the organs in an animal are.

Example 1: Water moving in a plant. – Both the root and shoot system play a role in moving water through the plant. – The roots can push water a few meters up the plant – however many plants are over 100 m tall, so the plant needs more than just the roots to push the water against gravity up the xylem to the leaves. – The key to moving the water is called transpiration. – Transpiration is the evaporation of water through the stomata in the leaves.

– Remember that water is a polar molecule and they are attracted to each other. When water evaporates from the leaves, it creates tension that pulls the adjacent water molecule up the xylem. – Plants loose a large amount of water due to transpiration. An acre of corn looses over 400, 000 gallons of water in a growing season. This is why plants need water on a consistent basis.

Example 2: Enduring Changes in the Environment – In cases of environmental changes, hormones in the plant are delivered to specific tissues. – When the amount of sunlight increases, these chemical messengers are delivered to stimulate flower production. – In times of drought or excessive heat, a plant may decrease its production of leaves, so excessive water is not lost through the stomata.