Biology: Plant Organs

Question 1

What is an organ?

Answer 1

An organ is a group of different tissues that perform a specific function, as well as a common function

Question 2

What are the main functions of leaves?

Answer 2

☆ Trap sunlight for photosynthesis

☆ Allow gaseous exchange to take place through the stomata for photosynthesis, respiration and transpiration

☆ Transports water and produced nutrients

Question 3

Define the term “transpiration”

Answer 3

Transpiration is the loss of water vapour through the aerial parts of the plant

Question 4

List the external structure of the leaf?

Answer 4

● A typical leaf usually consists of a large, flat lamina (leaf blade) that is attached to the stem of the plant by means of petiole (leafstalk)

● In the axil, between the stem and petiole, an auxiliary bud develops out of which lateral branches or flowers grow

● The veins of the leaf blade consist of xylem and phloem that are continuous with the xylem and phloem of the root ans stem

Question 5

Refer to the epidermis to list the internal structure of a leaf.

Answer 5

》Epidermis:
▪︎ The upper and lower surfaces of the leaf are covered by an epidermal layer
▪︎ The epidermis protects the underlying tissues
▪︎ Regular epidermal cells do not contain chloroplasts and are transparent in order to allow light through to the underlying tissues for photosynthesis
▪︎ A waxy, transparent cuticle covers the epidermis, reducing3 excessive moisture loss while allowing sunlight through for photosynthesis
▪︎ The lower epidermal cells contain stomata. The gaurd cells of the stoma are responsible for the opening and closing of the stomatal pore. Stomata are responsible for gaseous exchange into and out of the leaf during:
☆ photosynthesis: CO2 in and O2 out by diffusion
☆ respiration: O2 and CO2 out by diffusion
☆ transpiration: Water vapour out by diffusion

Question 6

Refer to the mesophyll to list the internal structure of the leaf

Answer 6

☆ Two types of mesopyll cells, ie: palisade and spongy mesophyll cells, fill the space between the upper and lower epidermis

PALISADE MESOPHYLL CELLS:
》These are elongated, thin-walled parenchyma cells are situated just under the upper epidermis

》 The cells contain a large number of choroplasts, thus enabling them to absorb the maximum amount of sunlight for photosynthesis

》 The cells are arranged longitudinally and packed tightly against one another, without intercellular spaces. This ensures that the largest possible surface area is exposed to sunlight for photosynthesis

》 The cells are very thin for easy diffusion of gases (CO2 and O2) into and out of the cells during photosynthesis and cell respiration

SPONGY MESOPHYLL CELLS:

》 This is the lower mesophyll layer

》 The cells are round parenchyma cells, loosely packed in an irregular manner

》 They contain large intercellular spaces that are connected to the air chambers behind the stomata for gaseous exchange

》 These cells contain choroplasts for photosynthesis, but fewer than the palisade mesophyll cells

Question 7

Refer to the vascular bundles/veins to list the internal structure of a leaf

Answer 7

♡ The veins consist of xylem and phleom that are continuous with the xylem and phloem of the root and stem

♡ Water that is absorbed from the soil and transported via the root and stem, xylem to the leaf moves by Osmosis until it reaches the mesophyll cells, where it is used for photosynthesis

♡ The phloem transports organic nutrients, which are manufactured in the leaf during photosynthesis, to other parts of the plant