These questions ask what roots obtain, how root hair cells absorb it, and what happens when important mineral ions are scarce. Keep three ideas separate: the material entering, the process that moves it, and the use the plant makes of it.
Match material, process and purpose
Roots spread through soil for anchorage and absorption. Each root hair is a long, narrow extension that increases membrane area in contact with soil moisture. That moisture moves across the cell membrane by osmosis, down its concentration difference without an energy supply. Mineral ions can be less concentrated outside than inside the cell, so taking them in against that difference requires active transport powered by respiration. Root cells respire by day and by night.
| Clue | Decision |
|---|---|
| Soil moisture crossing into a root hair | Use osmosis; this is passive movement across a membrane. |
| Mineral ions moving against a concentration difference | Use active transport and include energy released by respiration. |
| Poor growth and too little new tissue | Check nitrate supply because nitrates are needed to make amino acids and proteins. |
| Loss of green colour in leaves | Check magnesium supply because magnesium is needed to make the green pigment. |
| A fertiliser claim | Treat fertiliser as a source of mineral ions, not energy or ready-made food. |
Use symptoms as a chain of cause and effect. A shortage of nitrate limits protein production and therefore the building of new tissue, leading to stunted growth. A shortage of magnesium limits production of green pigment, so foliage becomes yellow. Light supplies energy for photosynthesis, and the plant stores that energy in organic fuel it makes itself. Soil contributes moisture and mineral raw materials. Ordinary underground root hair cells receive no light and therefore have no chloroplasts.
Avoid these root and mineral mix-ups
| Tempting idea | How to reject it |
|---|---|
| Calling ready-made organic fuel a root uptake | Separate raw materials from food. Roots absorb moisture and ions; green foliage manufactures its own fuel. |
| Saying the fine hair itself grips the plant in place | Its shape is suited to enlarging the absorbing surface. Anchorage comes from the spreading root system as a whole. |
| Using active transport for soil moisture | Ask whether the moving substance is moisture or an ion. Moisture crosses the membrane by osmosis without a cellular energy cost. |
| Linking nitrate directly to fuel, storage carbohydrate, or cell-wall material | Follow nitrate to amino acids and proteins. Photosynthesis can still make organic fuel when nitrate is missing. |
| Giving every plant cell chloroplasts | A buried absorbing cell has no light to capture. Chloroplasts belong in cells exposed to light, not automatically in every plant cell. |
Try it
Mineral ions are often scarcer in soil water than inside a root hair cell, and yet the cell keeps taking more of them in. How does it manage that, and what does it need?
- By osmosis, which costs the cell no energy
- By diffusion, helped along by the thin cell wall
- By active transport, using energy released in respiration
- By dissolving them in the sugar that arrives from the leaves
A well-watered plant standing in good light has grown to a normal size for its age, but its leaves have turned yellow. A shortage of which mineral best explains that, and why?
- Nitrate, because the leaves cannot make enough protein
- Magnesium, because the leaves make too little chlorophyll
- Neither, because yellowing always means too little water
- Neither, because yellowing always means too little light