B5. Plant Nutrition

 (0654) Coordinated Sciences 2023/2024

Subheadings and Key concepts

• photosynthesis
• investigating the need for
• chlorophyll
• light
• CO2
• investigating the rate of photosynthesis
• light intensity
• temperature
• leaf structure and function
• photosynthesis
• gas exchange
• transport
• importance of magnesium and nitrate ions

B7.1. Transport in Plants

Within the vascular bundle, the xylem transports water and minerals, while the phloem transports sucrose and amino acids (translocation). Water is absorbed into the roots through root hair cells, then moves up the plant by transpiration, and eventually leaves the plant by evaporation.

B7.1. Transport in Plants

(0654) Coordinated Science syllabus

*many images and illustrations courtesy of Save My Exams and other sources.

06. Plant Transport pdf

#68 Summary of plant transport

In plants, xylem vessels transport water and mineral ions from the roots upwards to the leaves. Phloem tubes transport sucrose and other organic nutrients, from the leaves where they are made to all parts of the plant. This is called translocation.

#67 Transport of materials from sources to sinks at different seasons

'Source' is the part of a plant where substances are produced (e.g. leaves for sucrose, amino acids) or enter the plant.

'Sink' refers to the part of the plant where the substrate can be stored (e.g. roots or stem for starch).

#66 Translocation of applied chemicals (pesticides) throughout the plant

People who grow crops for food sometimes need to use chemicals called pesticides. Pests such as insects that eat the crop plants, or fungi that grow on them, can greatly reduce the yield of the crop. Pesticides are use to kill the insects or fungi.

# 65 Translocation of organic foods in plants

Translocation is the movement of organic food such sucrose and amino  acids  in phloem; from regions of production to regions of storage OR regions of utilisation in respiration or growth.

#64 Adaptations of the leaf, stem and root to different environments

Plants which live in extreme environments have adaptations to control their transpiration rate. Most modifications are adaptations to very dry (arid) environments. 

Water plants have no problems of water shortage.  They do not need adaptations to conserve water as desert plants.  

# 63 Transpiration in plants and factors affecting transpiration rate

In the leaves, water molecules leave the xylem vessels and move from cell to cell. They move through the spongy mesophyll layer by osmosis along a concentration gradient. Water then evaporates into spaces behind the stomata and diffuses through the stomata into the surrounding air.

#62 Passage of water through root, stem and leaf

Water enters root hair cells by osmosis. This happens when the water potential in the soil surrounding the root is higher than in the cell à water diffuses from the soil into the root hair, down its concentration gradient.

# 61 Root hairs and water uptake by plants

Plants take in water from the soil, through their root hairs: 

At the very tip is a root cap. This is a layer of cells which protects the root as it grows through the soil. 

The rest of the root is covered by a layer of cells called the epidermis.

The root hairs are a little way up from the root tip. Each root hair is a long epidermal cell. Root hairs do not live for very long. As the root grows, they are replaced by new ones. 

#60 Distribution of Xylem and Phloem in roots, stems and leaves

Root

In the roots, xylem and phloem are in the centre to withstand stretching forces. 

#59 Transport in plants - functions of xylem and phloem

Plants have transport systems to move food, water and minerals around. These systems use continuous tubes called xylem and phloem:

- Xylem vessels carry water and minerals from the roots to the leaves.  

- Phloem tubes carry sugar & other organic nutrients made by plant from the leaves to the rest of the plant.