Mrs RagsdaleBiology HL

Ground tissue◦ Basic survival functions for plant,

such as gathering of water and nutrients

◦ Storage Vascular tissue (think arteries

and veins)◦ Distribution of water and dissolved

nutrients Dermal tissue (think plant skin)

◦ Protection and covering of plants

http://www.phschool.com/science/biology_place/biocoach/plants/tissue.html

Parenchyma◦ Pliable, soft, thin-walled cells that make up the

tissue where primary growth takes place◦ Site of gas exchange in leaves◦ Used for storage and secretion

Collenchyma◦ Support cells that are typically long and flexible◦ Appear primarily in lengthening stems and stalk ribs

Sclerenchyma◦ Thick, stiff walls that are made stronger by adding

lignin◦ Waterproofs the cell ◦ Adds protection

Fibers or sclerids

http://kids.britannica.com/comptons/art-53828/Parenchyma-tissue-makes-up-most-of-the-pith-and-cortex

Vascular – Transport system◦ Xylem – Transports from the roots to the stems

Also offers mechanical support◦ Phloem – Transports from the stems to the roots

Dermal – Outer protection (skin)◦ Epidermis – covers surfaces of the plant◦ Cuticle – thick waxy covering◦ Stoma (Stomata plural) – “pores” or the openings

along the epidermis for gas exchange

Connect leaves roots and flowers Vital role in transport – location of xylem

and phloem Support aerial portion of plant

◦ Cell turgor – cells absorb water until they are under high pressure. This high pressure helps give support by making the cells rigid

◦ Cell walls in xylem have lignin in them making them extremely strong In woody stems, xylem especially gives support

Plant’s version of “stem cells” Meristem tissue is always going to be the

site of plant growth and cell differentiation Apical meristem – located at the tips of

stems and roots Lateral meristem – dicotyledonous plants

are able to grow outwards as well as upwards. The lateral meristem develops between xylem and phloem and allows this outwards growth.

Apical meristem Dicotyledonous Plant

Dicot Stem Cross Section

Site of photosynthesis◦ Leaf structure related to function – designed to

maximize exposure to sun◦ Location of chloroplasts

Site of transpiration◦ Designed to protect from losing too much water

during the heat of the day

http://www.enchantedlearning.com/subjects/plants/leaf/

Leaf blade (lamina) – main part of the leaf, designed to absorb sunlight

Palisade mesophyll – densely packed cylindrical cells with a large amount of chloroplasts

Spongy mesophyll – loosely packed rounded cells with few chloroplasts, main site of gas exchange in the tissue

Stoma – pores that open and close, site of gas exchange

Guard cells – the “muscular” cells that open and close the stomata

Upper epidermis – continuous layer of cells covered by a thick waxy cuticle

Basic job of roots is to absorb water and minerals from soil

Roots increase surface area by branching off and growing root hairs

Concentration of minerals is typically greater in the root than in the soil so active transport methods are used◦ This takes ATP!◦ Roots typically have mitochondria to

assist with active transport

1. Diffusion of mineral ions2. Fungal hyphae (mutualism)

◦ Fungus grows near the roots of the plant

◦ Mutualistic relationship because both fungus and plant benefit

3. Mass flow of water in the soil carrying ions when water drains through the soil

No plasma membranes so water is free to move

Cells are “dead” at maturity and hollow

Sieve tubes allow water to move out of the xylem vessel and into the cell walls of leaves

Xylem moves water and dissolved minerals up from the roots to the leaves

How does xylem manage to pull water up its empty tubes?◦ Continuous flow of water during transpiration –

transpiration stream◦ Transpiration pull – low pressure suction inside

the xylem vessel caused by capillary action◦ Cohesion – water molecules tend to pull tightly

together because of hydrogen bonding◦ Adhesion – water sticks to the walls of the xylem

because of its adhesive nature

Phloem flows from the leaves (the site of photosynthesis aka the candy shop) down to the roots

Active transport of sugars and amino acids The places where sugars are made are

called sources and taken down to the roots also called sinks

Monocotyledon – one baby seed leaf

Dicotyledonous – two baby seed leaves

Leaf veins run parallel to each other

Vascular bundles spread randomly in the stem

Stamens, flowers and other organs are in multiples of 3

Unbranched roots grow from stems

Leaf veins form net-like patterns

Vascular bundles in a ring near the outside of the stem

Stamens, organs and flowers in multiples of 4 or 5

Roots branch off from other roots

Bulbs – underground organs that are made from leaf bases◦ Used for food storage◦ Monocotyledon plants◦ Serioes of leaf bases fitting

inside each other with a central shoot apical meristem

Storage Roots◦ Some roots swell up with

stored food◦ Typically have vascular

tissue in the centre

Stem tubers◦ Dicotyledon plants◦ Plant stems grow

downward into the soil◦ Sections then grow

into stem tubers which are used for food storage

◦ Identified as stems because their vascular bundles are in a ring

Tendrils◦ Narrow outgrowths

from leaves that create a corkscrew

◦ Once they touch a support, they attach to it

◦ Used by the plant to grow upwards

Transpiration MUST be controlled or plants will lose too much water

Abscisic acid – release causes guard cells to close which then close the stomata

Plants produce abscisic acid when they are dealing with water stress

Light – typically stomata open during light and close at night

Temperature – heat needed to make water evaporate◦ High temperatures = higher rates of transpiration◦ Lower temperatures = lower rates of transpiration

Humidity – lower humidity leads to higher rates of transpiration

Wind – higher wind increases transpiration rates

Plants adapted to dry habitats CAM plants – stomata open during

the night and not the day◦ Light dependant reactions occur during

they day◦ Light independent reaction occurs at

night Stems tend to be vertical to absorb

early sunlight Spines instead of leaves to reduce

surface area Thick waxy cuticles to keep water

in

http://www.bbc.co.uk/gardening/basics/techniques/houseplants_cactus1.shtml

Reduced leaves into spines Thick waxy cuticles Reduced number of stomata Deep root systems Water storage tissue CAM physiology – adaptation to

photosynthesis