9.1 Plant structure & growth

Assessment Statement 9.1.1 Draw and label plan diagrams to show the distribution

of tissues in the stem and leaf of a dicotyledonous plant.9.1.2 Outline three differences between the structures of

dicotyledonous and monocotyledonous plants.9.1.3 Explain the relationship between the distribution of

tissues in the leaf and the functions of these tissues.9.1.4 Identify modifications of roots, stems and leaves for

different functions: bulbs, stem tubers, storage roots and tendrils.

9.1.5 State that dicotyledonous plants have apical and lateral meristems.

9.1.6 Compare growth due to apical and lateral meristems in dicotyledonous plants.

9.1.7 Explain the role of auxin in phototropism as an example of the control of plant growth.

Draw a labelled plan diagram to show the distribution of tissues in the stem of a dicotyledonous plant

Structure Function

Epidermis Thin layer of cells for protection

Xylem For transport of water & mineral ions

Phloem For translocation of organic nutrients such as amino acids & sucrose

Pith Storage and support

Cambium layer of actively dividing cells (lateral meristem ) for the secondary growth

Cortex Packaging tissue for storage and support

Draw a labelled plan diagram to show the distribution of tissues in the leaf of a dicotyledonous plant.

Differences between the structures of dicotyledonous & monocotyledonous plants

Monocotyledons DicotyledonsParallel veins in narrow leaves Branching, net-like veins in broad

leaves

Embryo has ONE cotyledon Embryo has TWO cotyledons

Flower parts (sepals & petals) arranged in threes

Flower parts (sepals & petals) arranged in fours or fives

Fibrous adventitious roots Tap root with lateral branches

Vascular bundles scatted throughout the cortex

Vascular bundles arranged in a ring around edge

E.g. maize, wheat, oat E.g. bean, daisy, sunflower, pea

Relationship between the distribution of tissues in the leaf & their functions

Relationship between the distribution of tissues in the leaf & their functions

palisade cells contain lots of chloroplasts for absorbing light energy

palisade cells arranged “end-on” to ensure each cell receives maximum amount of light

no chloroplasts in upper epidermis to ensure light reaches palisade layer

chloroplasts present in spongy mesophyll cells to ‘mop up’ any unused light

waxy cuticle to prevent excessive water loss from epidermal cells by evaporation

air spaces in spongy mesophyll layer to ensure adequate supply of CO2 to photosynthesizing cells and ease of removal of O2

stomata located on leaf lower surface to allow gases in and out of leaf

presence of vascular bundle to supply water from roots & for removal of products of photosynthesis

Modifications of roots, stems and leaves for different functions

Bulbsbulbs are underground

storage structures that contain reserves of nutrients to ensure survival from season to season

consists of layers of fleshy leaf bases closely packed on a short stem

the leaf cells are packed with starch grains & other nutrients

E.g. onion, garlic

Stem tubers stem tubers are

swollen tip of rhizome or underground stem

they store carbohydrate for growth of new plants during the next season

the cortex cells in the stem are packed with starch grains & other nutrients

E.g. Irish potato

Storage roots storage roots

contain stores of carbohydrate for the plant to use later

they are usually swollen tap roots (primary roots)

the cortex cells in the root are packed with starch grains & other nutrients

e.g. carrot, sweet potato

Tendrilstendrils are modified

leavestendrils are slender

stem-like structure to curl around to a support

they are sensitive to touch, so faster growth occurs on the opposite side

tendrils help support the plant

E.g. vine, ivy

Apical and lateral meristemsplants grow at meristems i.e.

regions of unspecialised cells that retains ability to divide & differentiate into any type of cells

after cytokinesis, one daughter cell differentiates & the other remains in the meristem

dicotyledonous plants have apical & lateral meristems

apical meristems, are found at the tips of shoot & root, they result in growth in length of the plant – primary growth

lateral meristems, are found at the tips of cambium in the vascular bundles, they result in increase the diameter or girth of the plant – secondary growth

Phototropismphototropism is plant's

response to directional light by either growing towards it or away from it

there are two types of phototropism: positive phototropism,

i.e. growth of a plant’s shoot towards light, putting the leaves in a better position for photosynthesis

negative phototropism, i.e. growth of a plant's roots away from light

phototropic responses are controlled by auxins, plant growth hormones

Role of auxin in phototropism auxin is a plant hormone produced by

the tip of the shoot (stem) auxin causes transport of hydrogen ions

(H+) from cytoplasm to cell wall decrease in pH due to H+ pumping

breaks bonds between cell wall fibres, making cell walls flexible & extensible

auxin makes cells enlarge, elongate & grow

gene expression is also altered by auxin to promote cell growth

in positive phototropism, growth occur towards the source of light

shoot tip senses the direction of brightest light, auxin are moved to side of stem with least light i.e. darker side

higher concentration of auxin causes cells on dark side to elongate & grow faster than on the illuminated side - hence the shoot bends towards the source of light

any questions on plant structure & growth

Thank you