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