Plant Structure & Function (Edexcel International A Level (IAL) Biology): Flashcards

An amyloplast is a small, membrane-bound organelle in plant cells that contains starch granules and is especially abundant in storage organs like potato tubers.

Amyloplasts are responsible for storing starch in plants and converting it back to glucose when needed.

The vacuole keeps plant cells turgid, stores various substances, and breaks down unwanted chemicals, while the tonoplast controls what enters and leaves the vacuole.

Electron microscopy of plant cells is the use of a transmission electron microscope (TEM) to observe and identify plant organelles in detail by examining their structure and arrangement.

The chloroplast contains distinctive stacks of thylakoids and has a double membrane.

A vacuole usually appears as a large, light area inside a plant cell on an electron micrograph and indicates the cell is a plant cell.

The nucleus is a roughly spherical organelle surrounded by a nuclear membrane and contains a dark nucleolus within.

True.

Mitochondria have visible cristae (folds of the inner membrane), which are not seen in chloroplasts.

The cell wall is found around the outside of a plant cell and gives the cell structural support.

The cell membrane appears as a thin, dark line just inside the cell wall, following its inner edge. It encloses the cytoplasm and all of the cell's contents.

A TEM (transmission electron microscope) produces high-resolution 2D images of a cell's internal structure, whereas an SEM (scanning electron microscope) produces 3D images of the cell's surface.

Starch is a storage polysaccharide found in plants, composed of long chains of α-glucose monomers and stored as granules in plastids.

Starch is constructed from two different polysaccharides: amylose and amylopectin.

Amylose has an unbranched, helix-shaped structure with only 1,4 glycosidic bonds, while amylopectin is branched due to additional 1,6 glycosidic bonds.

Because starch is insoluble and compact, it can be stored in large quantities in plant cells without causing an osmotic effect.

True.

Amylopectin has 1,4 glycosidic bonds in the main chain and 1,6 glycosidic bonds at the branch points.

Cellulose is a polymer of β-glucose molecules joined by 1,4 glycosidic bonds, forming long, strong chains that provide structural support in plant cell walls.

Cellulose molecules are able to form many hydrogen bonds between chains, giving them great strength.

Every second β-glucose molecule must be rotated 180° to allow the formation of 1,4 glycosidic bonds between them.

Cellulose gives plant cell walls their high tensile strength and allows them to withstand turgor pressure.

False.

Most animals cannot digest cellulose because they lack the enzymes needed to break β-glycosidic bonds.

A sclerenchyma fibre is a long, hollow plant cell with thickened, lignified walls, providing strength and support to plants.

They are hollow because their cell contents died during development, often due to lignification of the cell wall, making it impossible for substances to enter or leave.

Plant fibres such as flax and hemp are used to make rope.

True.

The arrangement of cellulose microfibrils and the development of a thick, lignified secondary cell wall are the main reasons for the high strength of plant fibres.

Lignification is the process in which lignin is deposited in the cell walls, making them thicker and more rigid.

Secondary thickening in plant fibres often involves the deposition of lignin in the cell wall.

A cellulose microfibril is a bundle of cellulose chains. Their arrangement in a mesh-like (net-like) pattern within the cell wall is a key reason why plant fibres are so strong.

Plant fibres are renewable and biodegradable, so using them reduces reliance on non-renewable, oil-based synthetic materials.

Translocation is the movement of organic compounds (assimilates), particularly sucrose, through the phloem tissue from sources to sinks, both up and down the plant.

The main function of sieve tube elements is to transport organic compounds such as sucrose throughout the plant via the phloem.

Companion cells control the metabolism of sieve tube elements and are involved in loading and unloading sugars into the phloem.

Phloem tissue is made up of several cell types, but its bulk is composed of sieve tube elements and companion cells.

False.

Phloem tissue has no support function in a plant; it is involved in transport of organic compounds.

A xylem vessel is a long, hollow tube formed from dead cells with lignified walls, responsible for the transport of water and minerals and providing support in plants.

Lignin provides structural support to xylem vessels and enables them to withstand the pressure of the moving water column.

The main role of xylem tissue is to transport water and dissolved minerals around the plant.

False.

Xylem vessels are formed from dead cells and do not contain cytoplasm or organelles.

A sclerenchyma fibre is a long, hollow tube made of dead cells with lignified cell walls that provide structural support to plants.

Sclerenchyma fibres are associated with vascular bundles and provide support to the plant.

The lignification of sclerenchyma fibre cell walls provides them with strength and structural support.

The two main functions of plant stems are to provide support and to transport materials around the plant.

A vascular bundle is a structure in plant stems containing xylem, phloem, and sometimes sclerenchyma fibres, responsible for transport and support.

In a stem, xylem is found towards the middle, while phloem is closer to the outside.

False.

Mature xylem tissue is composed of dead cells, whereas mature phloem tissue contains living cells.

A permanent pre-prepared slide is a microscope slide that has already been prepared and fixed, allowing repeated examination of tissue types without further preparation.

To avoid trapping air bubbles, the cover slip should be lowered slowly over the sample from one side to the other.

A suitable stain is used to highlight different tissue types in the plant stem, making them easier to identify under the microscope.

Toluidine blue O stains xylem and sclerenchyma fibres blue-green, and phloem will appear pinkish purple.

A plan diagram is a simple, large-scale drawing of tissue distribution in a plant section, showing the general arrangement of tissues without individual cell details.

False.

When drawing a plan diagram from a high-power image, only a few of the required cells should be drawn, not every individual plant cell.

To prepare a temporary slide of a plant stem cross-section, you need a scalpel, suitable stain, microscope slide, cover slip, forceps, dissecting needle, light microscope, and gloves.

When labelling a plan diagram, label lines should stop exactly at the structure and should not cross over each other.