Lesson Notes By Weeks and Term v5 - Grade 8

Lesson Video

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Performance objectives

• Describe xylem and phloem in plants.
• Explain the human circulatory system (heart, blood, vessels).
• Compare transport systems in plants and animals.
• Understand diffusion and osmosis.
• Explain why efficient transport is vital for survival.

Lesson summary

This week, we delve into the fascinating world of transport systems in plants and animals. Imagine trying to build a house without a road to bring in bricks or a way to carry away waste. Similarly, living organisms need efficient systems to transport essential substances like water, nutrients, oxygen, and waste products throughout their bodies. Understanding these systems is crucial because it explains how plants grow, how animals function, and even how diseases spread. Think about the food you eat – it needs to be transported around your body to provide energy. Or consider the water farmers use to irrigate crops – it needs to reach every part of the plant to ensure healthy growth.

Lesson notes

2.1 Transport in Plants Plants need to transport water and nutrients from the soil to the leaves and sugars (produced during photosynthesis) from the leaves to other parts of the plant for growth, storage, and respiration. This is accomplished through two main types of vascular tissue: xylem and phloem.

Xylem: Xylem is responsible for transporting water and dissolved minerals upwards from the roots to the rest of the plant. Think of it as the plumbing system of the plant. Xylem vessels are essentially dead cells arranged end-to-end to form long, hollow tubes. Their walls are strengthened by a substance called lignin, which provides support to the plant and prevents the vessels from collapsing. The movement of water through the xylem is largely driven by transpiration (the evaporation of water from the leaves), creating a 'pull' that draws water upwards. This process is also aided by cohesion (water molecules sticking together) and adhesion (water molecules sticking to the xylem walls).

Phloem: Phloem transports sugars (produced during photosynthesis in the leaves) to other parts of the plant, such as the roots, stems, and fruits. This is known as translocation. Phloem consists of living cells called sieve tubes and companion cells. Sieve tubes are arranged end-to-end, forming long tubes, but unlike xylem, they have perforated end walls called sieve plates, which allow the movement of sugars from one cell to another. Companion cells are closely associated with sieve tubes and provide them with energy and support. The movement of sugars through the phloem is an active process, requiring energy from the plant.