Plant Structures Flashcards
What are the three main plant structures?
Root
Stem
Leaf
How can you tell that a cross section is that of a root?
It will have root hairs
It will have vascular tissue in the form of a cross
It will have a thicker endodermis
How can you tell that a cross section is that of a stem?
It will have vascular bundles
It will have pith
It has quite a thin endodermis
What is the function of the root?
Absorb water and mineral salts from soil
Anchors the plant in the soil
What are the two root systems?
Tap root system
Fibrous root system
What are the five regions of a root?
Mature region Root hair region Region of elongation Meristematic region Root cap
What is Spring wood?
Secondary xylem
Is lighter and bigger, because it forms quickly
What is autumn wood?
Secondary xylem
Is darker and smaller, because it forms slowly
What is cork?
The outer bark of the tree
How does cork form?
The parenchyma tissue becomes meristematic
What makes bark so strong?
It is reinforced with suberin
What are angiosperms?
Flowering plants
What is the most advanced group in the plant kingdom?
Angiosperms
What two groups can angiosperms be divided into?
Monocotyledons
Dicotyledons
What is the function of the root cap?
Surrounds and protects the growing point
What is the function of the meristematic region?
Continuously forms new cells
What is the function of the region of elongation?
New cells elongate in this region
What is the function of the root hair region?
The place where root hairs (unicellular epidermal outgrowths) occur
What is the function of the mature region?
Where lateral roots develop and branch
What is the function of the lateral roots?
Increase absorption surface
Anchor the plant more firmly in the soil
What three regions occur within a root?
Epidermis
Cortex
Central cylinder
Where does the epidermis of a root occur?
On the outside
What does the epidermis consist of?
Epidermal cells
Root hairs
Where can the cortex of the root be found?
In the middle section of a root
What are the components of the cortex?
Parenchyma
Endodermis
Where does the central cylinder of a root occur?
In the innermost ring
What are the components of the central cylinder?
Pericycle
Xylem
Cambium
Phloem
Where can the root be found?
In the soil
It is dark
There are micro and burrowing organisms found here
What is the root cap made of?
Thin walled parenchyma cells
How does the root cap perform its function?
Fluid nature of protoplasm lubricates passage of root apex
How does the root grow?
Elongating cells push the root tip further in the soil
What is the outer layer of a root hair like?
Sticky to adhere to soil particles
What are the functions of the cortex parenchyma?
To store food
Allow water and mineral salts to pass through
Diffuse oxygen
How does the endodermis occur?
As parenchyma cells
Border between the cortex and central cylinder
Has Casparian strips on the radial and transverse walls
What is a Casparian strip?
A thickened cork part of the cell walls in the endodermis
What is the function of the Casparian strips?
Direct water straight into the xylem
What is the pericycle?
Parenchyma cells
They give rise to secondary (lateral) roots
Where is the vascular tissue located?
Within the pericycle
How is the vascular tissue arranged?
Xylem in the form of a cross
Phloem between the ‘arms’ of the cross
What is the function of the root xylem?
Transportation of water and mineral salts from the root to the rest of the plant
Lignified walls strengthen the plant and give it structure
What is the role of cambium cells?
In a dicotyledonous plant, they occur between xylem and phloem
They cause secondary thickening
What is the function of phloem?
Transportation of manufactured organic substances throughout the plant
What are the main functions of a stem?
Bears the leaves Bears the flowers Bears fruits Transportation of essential substances Stores reserve nutrients and water
What does the external structure of a stem consist of?
Nodes
Internodes
Terminal buds
Axillary buds
What is a node?
Where the leaves and side branches develop
What is the internode?
The part of a stem between nodes
What are buds?
Meristematic tissue in the stem
What is the terminal bud?
Occurs at the tip of the stem
What is the function of the terminal bud?
Primary growth (increases the length of the plant)
Where can the axillary buds be found?
In the axils between the petiole and the stem
What is the function of the axillary buds?
To develop flowers
Or lateral branches
What three areas can be seen in a dicotyledonous stem?
Epidermis
Cortex
Central cylinder
What does the epidermis of a stem consist of?
Cuticle
Hairy outgrowths
Epidermal cells
What does the stem cortex consist of?
Collenchyma (in some stems)
Parenchyma
Endodermis
What does the central cylinder consist of?
Sclerenchyma cap Phloem Cambium Xylem Medullary ray
What is the function of the cuticle?
Waterproof
Prevent bacteria from entering
Minimise water loss
What is the function of the epidermis?
Act as a barrier between environment and external tissues
What is the difference between hairy outgrowths on the stem and root hairs?
Root hairs: unicellular
Hairy outgrowths: multicellular
What is the function of collenchyma?
Extra support
Sometimes contains chloroplasts for photosynthesis
Sclerenchyma can play this role in some plants
What is the endodermis?
Brick-shaped cells that form the inner layer of the cortex
What is the difference in the endodermis of the root and that of the stem?
Root: easily distinguished
Stem: less distinguished and even absent
What is a starch sheath?
The endodermis of the stem when it stores starch
How are the vascular bundles arranged?
In a circle
Within the endodermis
What is the structure of a vascular bundle?
Xylem on the inside
Phloem on the outside
Cambium between them
Sclerenchyma on the outside of the phloem
What is an open vascular bundle?
A vascular bundle that contains cambium
What are the medullary rays?
Parenchyma cells that occur between the vascular bundles
What is the function of the medullary rays?
Transportation between the pith and the cortex
What is the pith?
Parenchyma cells at the centre of the stem
What can sometimes happen to the pith during growth?
They rupture and leave a central cavity
What is the function of the sclerenchyma cap?
Protection of the vascular bundles
What is primary growth?
Increase in length
What is secondary growth/thickening?
Increase in girth
What is cambium?
Meristematic tissue for secondary growth
What is fascicular cambium?
Cambium that occurs between the xylem and phloem
What happens to parenchyma in the medullary rays during secondary growth?
Become meristematic
Called interfascicular cambium
What happens to the interfascicular and fascicular cambium during secondary growth?
They join up to form an unbroken ring
What is secondary vascular tissue?
Xylem and phloem rings that are formed from the cambium ring
What is primary vascular tissue?
The ‘original’ xylem and phloem in the stem
What happen to the primary xylem and primary phloem during secondary thickening?
They get pushed further away from one another
What are pith rays?
Parenchyma cells that extend from the middle of the stem outwards
How are pith rays formed?
Instead of forming vascular tissue, the cambium forms parenchyma
What are annual rings?
Rings of secondary xylem visible in a perennial stem
What do annual rings consist of?
Dark and light parts
What are the dark parts of annual rings?
Autumn wood
What are the light parts of annual rings?
Spring wood
How can you tell a tree’s age by the annual rings?
By counting the annual rings (spring wood & autumn wood together equate to one year of growth)
What kind of annual ring shows that the growth occurred during favourable conditions?
A thicker one
What is heartwood?
The oldest secondary xylem
It occurs furthest from the cambium
What is sapwood?
The youngest secondary xylem
It lies closest to the cambium
What is cork cambium?
Cortex collenchyma that has become meristematic
What does cork cambium do?
Divides
Forms cork cells on the outside
What are cork cells?
Have no living contents
Have walls thicken with Suberin
What is the function of cork?
It is impermeable to water
Prevents inner tissues from drying out
What happens to the epidermis when cork forms?
Stops receiving water and nutrients
Dies
Flakes off
What does the bark of a tree consist of?
Everything outside of the cambium ring
What tissues occur outside the cambium ring (in the bark)?
Secondary phloem Primary phloem Cortex Cork layer Flaking epidermis
What is a lenticel?
A section of the stem where cork cells separate with large intercellular air spaces
They form small pores that look like yellow speckles
Why are lenticels necessary?
They replace the stomata
i.e. They perform gaseous exchange
What are the main functions of the leaf?
Trap sunlight for photosynthesis
Gaseous exchange
Transportation of water and nutrients
Why is gaseous exchange important?
It is necessary for respiration, photosynthesis and transpiration
What are the parts of the external structure of the leaf?
Lamina Main vein Side vein Petiole Axillary bud
What is the lamina?
The large, flat ‘blade’ of the leaf
What is the petiole?
The leaf stalk
It attaches the lamina to the stem
What are the main and side veins?
Xylem and phloem tissue that is connected to the stem
What three section are visible in a cross section of a leaf?
Epidermis
Mesophyll
Vascular bundles (veins)
Where does the leaf epidermis occur?
On both the upper and lower surfaces of the leaf
What is the leaf epidermis like?
Transparent
Lower epidermal cells contain stomata
What is mesophyll?
Parenchyma cells found in the leaf
What are the two types of mesophyll?
Palisade
Spongy
Where are palisade mesophyll cells found?
Just beneath the epidermis
Where are spongy mesophyll cells found?
Beneath the palisade mesophyll cells
What is the structure of palisade mesophyll?
Elongated
Thin-walled
Lots of chloroplasts
How is palisade mesophyll arranged?
Longitudinally
Tightly packed
What is the function of the structure of palisade mesophyll?
Allow maximum surface area to be exposed to sunlight
Allow for a greater photosynthesising rate
What do spongy mesophyll cells look like?
Round
Loosely packed
Large intercellular air spaces that are connected to air chambers behind the stomata
Fewer chloroplasts
What is the function of the xylem in veins in the leaf?
Carry water to the mesophyll cells for photosynthesis
What is the function of phloem cells in veins?
Carry manufactured substances produced in the leaf to other parts of the plant
What is the midrib?
A continuation of the petiole into the leaf
What is the function of the midrib?
Same as veins
How is the lamina suited to its function?
Large and flat: max surface area
Thin: easy diffusion of gases
How is the cuticle suited to its function?
Waterproof: prevents water loss
Transparent: allows sunlight through
How are the epidermal cells suited to their function?
Transparent: allow sunlight through
Stomata (lower epidermis): gaseous exchange
