L1-3 -- The Roots

L1-3 -- The Roots

“Rapid Review” – Important terms and topics in this unit:

• Tissue systems are divided into ground, vascular and dermal tissues.

1) Ground Tissue: – Collenchyma cells: flexible and mechanical

support; found in stems and leaves.– Parenchyma cells: play a role in storage, secretion

and PS in cells.– Sclerenchyma cells: Protect seeds and support the

plant.

Supplementary notes:2) Vascular Tissue

• Xylem: transports water and minerals via transpiration – attractive forces between water molecules (cohesion) moves water from the root up, through the stem, into the leaves and throughout the plant. Water is used during PS, and lost to the environment through stomata.

• Phloem: Transports sugars and other nutrients around the plant.

Dermal Tissue:• The protective outer coating (epidermis) of

the plant stem, leaves and roots. Prevents water loss, protects from pathogens.

Roots (Draw in your notebooks)Taproot (dicots) vs. Fibrous (monocots)

Water movement into the roots

The Roots: The Importance of the Casparian Strip

• This band of specialized cells blocks water from moving between cells. Water and other solutes must move through cells of the endodermis to enter the vascular cylinder.

Water movement into the roots

Importance of the Casparian Strip

• This means the endodermis can control what enters the vascular cylinder (xylem and phloem), what doesn’t enter the cylinder, and how much.

Into the roots and beyond• Once inside the vascular cylinder, water can

move up the stem, and into leaves where it is lost to the environment (through the stomata) or used for PS!

Root Growth• The bottom of the root has a

root cap, which protects the root meristem as it divides and pushes the root down into the ground.

• It also secretes a slimy lubricant to push through soil more easily.

Root Growth

Zone of Cell Division and Elongation

• As cells divide, the root cap is pushed downwards (usually) through the soil. The root cap provides protection for the delicate meristem cells.

• Above the zone of division, cells start to elongate and push the root down further.

Zone of Maturation (differentiation)

• Cells become specialized here into different cell types, including root hairs, which absorb water and nutrients.

Questions to Answer (use complete sentences; answer in your notebooks):

1) Label the different types of tissues (ground, vascular and dermal) on the leaf diagram from last week. Label the roots; include the 3 growth regions (in different coloured ink).

2) Explain the difference between 1° and 2° growth.

3) Describe three advantages and disadvantages of a taproot vs. fibrous root system.

Exit Slip Question

• EXIT SLIPS: WRITE YOUR ANSWER IN COMPLETE SENTENCES ON THE EXIT SLIP PAPER. NO TALKING, COPYING, CHEATING.

• What is the importance of the root cap for the growth of roots through the soil?

Functions of the Root Cap

• 1) Protects the delicate meristem tissue.• 2) Secretes lubricants (called mucilage) to help the

root move through the soil more easily.• 3) The root cap produces hormones that guide the

root downwards. Growth in response to gravity is called gravitropism.– If the root cap is removed, sometimes the root will grow

in random directions.• Water / nutrients AREN’T absorbed by the root cap!

Further Notes: Growth Zones

• The zone of division, just above the root cap, has meristem tissue; this is where new root cells are produced.

• These cells become specialized later (as part of the vascular chamber, root hairs, part of the Casparian strip, or replacing damaged cells on the root cap.)

• Water / minerals aren’t absorbed here either!

Further Notes: Growth Zones

• The zone of elongation is where cells produced in the zone of division start to grow and elongate. This pushes the root downwards through the soil.

• Water / minerals aren’t absorbed here in this growth zone!

Zone of Differentiation / Maturation

• This is where cells from the zone of elongation become specialized.

• They will form the vascular cylinder, casparian strip, and other water-absorbing and transporting cells.

• The root hairs are what absorb water and minerals into the root of the plant!

Next: To the lab! – Germination of our seeds!

• Wash your hands when we get to the lab!!• Make notes of the date and time.• Make note of the ‘depth’ you planted the cells

in the little planters.• Take a picture!