Plant Power
Inside a leaf: the tissues that catch the light, the guard cells that breathe, and the pipes that carry water up and sugar out.
Revise this, the fun way
Play it interactively, earn XP and build a streak — free.
Start revising freeWhat you'll cover
Plant Power 🌿
A leaf looks flat and simple. Inside, it's a stack of specialised **tissues** — some catch light, some swap gases, some pipe water and sugar around the whole plant. Get each tissue matched to its job and you own one of Biology Paper 1's most reliable topics.
The tissues of a leaf 🧬
A **tissue** is a group of similar cells doing one job. In a leaf: • **Epidermal tissue** covers and protects the leaf; the upper layer is transparent to let light through, with a waxy **cuticle** to cut water loss. • **Palisade mesophyll** — tall cells packed with chloroplasts near the top: the main site of **photosynthesis**. • **Spongy mesophyll** — loosely packed with **air spaces** for gas exchange. • **Xylem** and **phloem** — the transport tissues. • **Meristem** — cells at the growing tips that divide to make the plant grow.
Match tissue to job
- Palisade mesophyll
- Spongy mesophyll
- Xylem
- Phloem
- Meristem
- Absorbs light for photosynthesis
- Air spaces for gas exchange
- Carries water and minerals up from the roots
- Transports dissolved sugars around the plant
- Dividing cells that make the plant grow
The leaf as an organ 🍃
An **organ** is several tissues working together. The leaf stacks them top to bottom: **waxy cuticle → upper epidermis → palisade mesophyll → spongy mesophyll → lower epidermis** — with **vascular bundles** (xylem + phloem) running through as veins. The order is not random: the light-catching palisade sits highest, the gas-swapping spongy layer sits near the stomata below.
Label the leaf
An interactive activity.
Why palisade sits on top
Palisade mesophyll cells are packed with chloroplasts and sit **near the top** of the leaf. Why is that position ideal?
- They receive the most light, so they can do the most photosynthesis
- It puts them closest to the stomata for gas exchange
- So water reaches them before any other cells
- To give the leaf its structural support
Stomata & guard cells 🕳️
The lower epidermis is dotted with tiny pores called **stomata** (singular: stoma), each surrounded by two **guard cells**. Stomata let **carbon dioxide in** and **oxygen out** for photosynthesis — but open stomata also let **water vapour escape**. The guard cells **open** the stomata in the light (for gas exchange) and **close** them to conserve water — a constant trade-off.
Find the stoma
An interactive activity.
Two flows: up and out 💦
The leaf drives two transport streams: • **Transpiration** — water evaporates from the leaf (mostly through the stomata), pulling a stream of water and minerals **up** the **xylem** from the roots. One direction only: up. • **Translocation** — dissolved **sugars** made in photosynthesis move through the **phloem** to wherever the plant needs them: **both** directions. Transpiration rate rises with more **light**, higher **temperature**, more **air movement** (wind), and **lower humidity**. A **potometer** measures the rate of water uptake.
Potometer maths
An interactive activity.
Turn up the rate
A plant is moved from still, humid air into a warm, windy spot. What happens to its transpiration rate?
- It increases — warmth and wind both speed up water loss
- It decreases
- It stays exactly the same
- It stops completely
In the exam 🎓
Leaf dissected. Grade-9 habits for plant organisation: • Link tissue to job **precisely**: **xylem** = water + minerals **up** (dead cells, **lignin** for support); **phloem** = sugars by **translocation**, **both** ways. • **Palisade** does most photosynthesis (top, packed chloroplasts); **spongy** mesophyll has air spaces for gas exchange. • **Potometer** questions test **controlling variables** and working out **rate = distance ÷ time**.