Transport in plants - Xylem and Phloem - GCSE Biology (9-1)

Summary

The script discusses the necessity of transport systems in organisms. Unicellular organisms rely on diffusion due to their large surface area to volume ratio. Multicellular organisms, exemplified by an oak tree, require a vascular system. Plants have xylem for water and minerals transport and phloem for sugars and amino acids. Xylem is composed of dead cells with lignin for strength, while phloem facilitates bidirectional translocation of photosynthesis products.

Takeaways

• 🌿 **Unicellular Organisms**: Single-celled organisms don't need transport systems as they obtain nutrients by diffusion through their cell membrane.
• 🌳 **Multicellular Organisms**: Larger organisms like oak trees require a transport system to supply all cells with necessary substances.
• 🍃 **Plant Vascular System**: In plants, a network of veins or vascular bundles transports substances from roots to leaves.
• 🔵 **Xylem Vessels**: Xylem vessels transport water and dissolved minerals from roots to leaves in a unidirectional flow.
• 🔴 **Phloem Vessels**: Phloem vessels transport sugars and amino acids, moving in the direction needed, up or down the plant.
• 📏 **Surface Area to Volume Ratio**: Unicellular organisms have a large surface area relative to their volume, facilitating efficient diffusion.
• 🚰 **Xylem Structure**: Xylem is composed of dead cells with hollow lumens, strengthened by lignin, for efficient water transport.
• 🌱 **Phloem Function**: Phloem translocates products of photosynthesis, such as sugars and amino acids, to where they are needed in the plant.
• 🌾 **Vascular Bundle Arrangement**: In a stem cross-section, vascular bundles are arranged around the outside, providing structure and support.
• 🍂 **Leaf Vein Structure**: Leaf veins branch into smaller ones to reach every cell, with xylem in the center and phloem around it.

Q & A

What is the primary mode of obtaining nutrients for unicellular organisms?

Unicellular organisms obtain nutrients by diffusion through their cell membrane, as they do not require complex transport systems like multicellular organisms.

Why don't unicellular organisms need a transport system?

Unicellular organisms have a large surface area to volume ratio, allowing them to efficiently exchange nutrients and waste directly with their environment without the need for a transport system.

What is the role of the transport system in multicellular organisms like an oak tree?

In multicellular organisms like an oak tree, the transport system is essential to supply all the cells with nutrients, water, and other necessary substances.

What are the two types of vessels found within a vascular bundle in plants?

The two types of vessels found within a vascular bundle in plants are the xylem vessels, which transport water and dissolved minerals, and the phloem, which transports sugars and amino acids.

How do the veins in a plant leaf facilitate transport?

The veins in a plant leaf branch into smaller ones to reach every single cell, ensuring that all parts of the leaf receive the necessary nutrients and substances.

What is the function of xylem in a plant?

The xylem in a plant transports water and dissolved minerals from the roots up through the plant to the leaves.

Why are xylem cells described as being made of dead cells?

Xylem cells are described as dead because they have had their cytoplasm and cell walls removed, creating a hollow lumen that allows for efficient water transport.

What substance strengthens the xylem cells to allow for the transport of water?

Lignin is the substance that strengthens the xylem cells, making them rigid and able to transport water effectively.

How does the phloem differ from the xylem in terms of transport direction?

Unlike the xylem, which transports substances in one direction (upwards), the phloem transports products of photosynthesis to all parts of the plant, moving upwards, downwards, or laterally as needed.

What substances does the phloem transport and for what purposes?

The phloem transports sugars (mostly sucrose) for energy and respiration, and amino acids for growth. These substances can also be stored in the roots as starch.

What is the term for the movement of substances within the phloem?

The movement of substances within the phloem is known as translocation.