Plants

What organelles are found in plant cells?

• Cell wall

• Middle Lamella

• Plasmodesmata

• Pits

• Chloroplasts

• Amyloplasts

• Vacuole and tonoplast

What is the cell wall?

• a rigid structure, outside the cell membrane, that provides structural support

• this structural support is provided by the polysaccharide cellulose

What is the middle lamella?

• outermost layer of the cell

• acts as an adhesive, helping stick to other cells

• gives the plant stability

What is the plasmodesmata?

•  plasmodesmata are narrow threads of cytoplasm (surrounded by a cell membrane) which connect the cytoplasm of neighbouring plant cells

• This allows:

→ substances to be transported between plant cells

→ facilitates cell to cell communication

What are pits?

• These are very thin regions of the cell wall

• The pits in adjacent plant cells are lined up in pairs

• This facilitates transport of substances between cells

What are chloroplasts?

• larger than mitochondria

• small and flat membrane bound compartments

• double membraned

• membranes inside called thylakoids,contaning chlorophyll, which stack to form grana

• grana linked by lamella membrane

• surrounded by thick fluid ( stroma )

• photosynthesis happens both partly in grana and stroma

• contain small circular peices of DNA and ribosomes → used to synthesis proteins needed in chloroplast replication and photosynthesis

What are amyloplasts?

• small organelle surrounded by a membrane

• contains strach granules

• stor strach grains

• covert starch into glucose when the plant needs it

What is the vacuole and tonoplast?

• a compartment surrounded by tonoplast membrane

• vacuole holds the cell sap, a mixture of water, minerals, enzymes and waste

• vacuoles keep the cell turgid → stops plants wiliting

• break down unwanted chemicals in the cell

• tonoplast controls what enters and leaves the vacuole

What is the structure of xylem vessels?

• made up of dead, hollow cells with no end walls.

• This forms one continuous tube when the xylem cells are stacked on top of each other

• no organelles or cytoplasm → creates more space inside for transporting water

• cell walls contain lignin which enables the vessels to withstand the pressure created by the moving column of water

Lignin is deposited in the cell wall → wall becomes thick, rigid, and waterproof → transport of substances into and out of the cell is cut off → the cell can no longer function → the cell dies → dead cells lose their contents → leaving a hollow lumen → cells join end-to-end → forming long, strong, hollow tubes → creating a continuous pipe for water transport

What is the function of xylem cellsi in plants?

• transport of water and mineral ions upwards through the stem (transpiration) AND support.

• Structural support

Where in the stem are xylem vessels found?

On the inside of the vascular bundle (towards the centre/pith).

What is the function of lignified cell walls in xylem vessels

• adds strength to withstand the hydrostatic pressure → so vessels do not collapse

• Lignin is hydrophobic and fills gaps in the cell wall, making it dense and impermeable to water

What is the function of no end plates in xylem vessels

• allows mass flow of water + dissolved solutes → since cohesive and adhesive forces aren’t impeded

What is the function of pits in xylem vessels?

• pits allow water to move sideways between neighbouring xyelm vessels or into surrounding tissues → water can be rerouted when one vessel becomes blocked e.g. by air bubbles

What is the function of the small diameter of vessels?

• helps prevent the water column from breaking and assits with capillary action

What is the function of phloem?

• Transport organic compounds (assimilates), particularly sucrose, from sources (e.g. leaves) to sinks (e.g. roots). The transport of these compounds can occur up and down the plant

• This is known as translocation

• Phloem has no support function in a plant, it is a living tissue

• made up of sieve tube elements and companion cells, each sieve tube element has a companion cell associated with it, as companion cells control the metabolism of their associated sieve tube member

Where in the stem in phloem found?

On the outside of the vascular bundle (between xylem and sclerenchyma fibres).

What are the structural compoments of the sieve tube elements and their function?

• sieve plates with pores → for continuous translocation of solutes through the plant

• made up of living cells → transloation requires energy due to bidirectional movement

• cellulose cell wall → strengthens the wall to withstand the hydrostatic pressures that move the assimlates

• no nucleus,vaucole,ribosomes ( Some ER and mitochondria present )→ maximises space for translocation

• thin cytoplasm → reduces friction to facilitate movement of the assimilates

What are the structural compoments of the companion cells and their function?

• nucelus and other organelles present → provides metabollic support to sieve tube elements, helps with loading and unloading

• transport proteins in plasma membrane → moves assimilates into and out the sieve tube elements

• large number of mitochondria → provides ATP for the active transport of assimiliates into or out of the companion cells

• plasmodesmata →link to sieve tube elements, allowing organic compound to move from companion cells into sieve tube elements

What is the function of scelernchyma fibres?

• Support ONLY – sclerenchyma fibres are NOT involved in transport.

What is the strcuture of scelernchyma fibres?

• Bundles of dead cells (similar to xylem) →no transport function allows full lignfication of cells

• Long, hollow tubes →support the stem along its entire length

• Hollow lumen + end walls present (unlike xylem) → strength and support

• Cell walls impregnated with lignin and high proportion of cellulose – very thick, rigid walls

• No pits (unlike xylem) – because they do not transport substances

• Long fibres run the length of the stem

What are vascular bundles?

made up of three key tissues: xylem, phloem, and sclerenchyma fibre

• xylem located towards middle of stem, phloem is closer outwards

What is the importance of water to plants?

• Required for photosynthesis (raw material)

• Transports minerals and dissolved substances throughout the plant

• Maintains turgidity in plant cells

• Regulates plant temperature through transpiration

What is the importance of magnesium ions for plants?

Central component of chlorophyll molecules

• Essential for photosynthesis (without it, photosynthesis cannot occur)

• Deficiency symptom: Leaves appear yellow (chlorosis) while veins remain green

What is the importance of nitrate ions for plants?

• Essential for synthesis of DNA, RNA, and proteins e.g. enzymes

• Required for chlorophyll formation

• Critical for plant growth, fruit production, and seed production

• Deficiency symptom: Leaves appear very pale/yellow

What is the importance of calcium ions for plants?

• Essential structural component of cell walls (forms calcium pectate in the middle lamella)

• Required for plant growth and development

• Helps maintain cell membrane integrity

How do plants obtain minerals?

• Minerals are dissolved in soil water

• Uptake occurs in root hair cells

• Mineral concentrations in soil are very low

• Plants must move minerals AGAINST the concentration gradient

• Therefore, ACTIVE TRANSPORT is used (requires ATP energy)

• Transportation around plant occurs via the XYLEM