Transpiration and Water Movement Revision Notes | GCSE OCR Foundation Biology

What this lesson covers

Understand the process of transpiration, the role of stomata and guard cells, and how environmental factors affect transpiration rate.

• Explain how transpiration occurs and its role in water transport through plants
• Describe the structure and function of stomata and guard cells in controlling water loss
• Analyse how environmental factors affect the rate of transpiration
• Calculate rates of transpiration using simple compound measures

Key ideas to keep in view

Use this lesson to stay inside B2.2 The challenges of size while connecting the detail back to the wider B2: Scaling up topic.

• B2: Scaling up
• B2.2 The challenges of size
• GCSE OCR Foundation Biology

Lesson notes preview

Read the core explanations from Transpiration and Water Movement before testing yourself from memory.

• Picture a 30-metre oak tree. Water enters through tiny root hairs in the soil and somehow travels all the way to the topmost leaves. No pump, no heart - yet water defies gravity every second of every day. This is transpiration in action, and it's one of the most elegant transport systems in nature.
• Understanding transpiration isn't just about plants - it connects to water cycles, climate, and even how we design greenhouses. Get this right, and you'll unlock how plants survive, thrive, and shape our world.
• 2. The Transpiration Process - Nature's Water Pump
• The loss of water vapour from plant leaves through stomata, creating a transpiration stream that pulls water up from roots through xylem vessels.
• Here's how the process works step by step. Water evaporates from mesophyll cells inside the leaf, creating water vapour. This vapour diffuses out through stomata - tiny pores on the leaf surface. As water leaves, it creates a 'pull' that draws more water up through the xylem vessels from the roots.
• Trap: Many students think plants actively pump water upwards. Actually, transpiration creates suction that pulls water up - like drinking through a very long straw. The plant doesn't push; evaporation pulls.
• Tiny pores on leaf surfaces, each surrounded by two guard cells that can open and close to control gas exchange and water loss.
• Guard cells are the gatekeepers. When they absorb water, they become turgid (swollen) and bend outwards, opening the stomata. When they lose water, they become flaccid and close the stomata. This gives plants precise control over when to lose water and when to conserve it.
• 3. Environmental Factors - What Speeds Up and Slows Down Transpiration
• Four key factors control how fast plants lose water. Understanding these helps explain why plants wilt on hot days and why greenhouses need careful climate control.

Continue through the topic

Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.