3.4 Flashcards
Why do structures have large surfaces compared to their volume?
Structures that function in absorption evolve to
have large surfaces
What structures evolve to have small surfaces compared to their volume?
Structures that function in storage
Structures with large surfaces relative to volume have __ of their cells exposed to the
environment and __ interior cells to which they
must __ materials.
more, fewer, transport
Large volumes compared to surface area is more efficient to store ___ and limits ___ to
the environment.
materials, exposure
What creates a large surface area for roots?
The extensive branching and the presence of root hairs
What is the roots outer cell layer?
Epidermis
Does root epidermis have a cuticle?
no
What do epidermal cells of the root produce?
Slender outgrowths known as root hairs
What is inside the epidermis?
Cortex
Where are xylem and phloem located?
in the center of the root, called the stele
What is the stele surrounded by?
Endodermis
What is the endodermis?
A layer of cells that controls the movement of nutrients into the xylem
How do water and minerals reach the xylem at the center of the root? How do they do this?
They move from soil through the root epidermis, cortex, and endodermis. They do this using diffusion, osmosis, and active transport
How do root epidermis cells pump ions into the root?
Active transport
What results when ions are pumped into the root?
It is now hypertonic and has a strong osmotic pull
What three ways can water and minerals move through the root cortex?
Symplast, transmembrane, and apoplast route
What happens during the symplast route?
Water and minerals move across the cell membrane of the root epidermis and move from cell to cell by interconnected cytoplasm.
What happens during the transmembrane route?
Water and minerals move across the cell membrane of the root epidermis and move from cells to cell across the cell membranes of the cortex cells
What happens during the apoplast route?
Water and minerals move between the root epidermis cells and around the cells through the extracellular spaces in cells walls
Can water and minerals move between the endodermis cells?
No, they must go throught the endodermis cells
How does water from the apoplast route reach the xylem?
It must pass through the cell membrane of an endodermis cell
What do endodermis cells do?
Regulate the passage of water and mineral ions
What does branching of root systems do?
Provide a large surface area for absorption
What do root hairs do?
Increase surface area even more
What does mutualisms with mycorrhizal fungi do?
Increase both water and mineral absorption
What does thick cortex act like?
A sponge to hold water
How do roots adapt to growth?
They are plastic and can grow differently depending on the environment
What do stems do?
Elevate and support flowers and leaves at different heights and serve as conduits between roots and leaves
How are stems similar to roots?
They are plastic and can grow differently under environmental conditions
What is stem epidermis covered by?
Waterproof cuticles or bark
Where is vascular tissue in stems?
Numerous bundles or layers
What do xylem and other lignified cells function as?
Rigid support
When did leaves evolve?
After roots and stems
What are leaves specialized for?
photosynthesis
What are megaphylls?
True leaves; thin photosynthetic tissue
How did early vascular plants photosynthesize?
Simple branching stems, it took place along the length of the shoot
What is the trade off for leaves?
It increases surface area for greater absorption of light and CO2, but it also means a greater surface area for water loss
Can some leaves be plastic?
yes
What does a leaf that grows in shade look like compared to one grown in the sun?
Shade leaves are thinner and larger, sun leaves are smaller and thicker
Does the volume of a leaf change depending on if it grows in sun or shade?
No, the volume will stay the same but the shape and width may change
Why are most leaves thin and flat?
To increase surface area
Why are the epidermis and cuticle transparent?
To allow light in
Why do guard cells contain chloroplast?
To make energy for the guard cells to work
What do vascular tissues in leaves form?
A network of veins
What are the photosynthetic tissue that contains air pockets called?
Spongy mesophyll
What is plasticity?
Plants responding to the world around them by modifying their size and shape
Cell division is confined to discrete populations of totipotent (undifferentiated) cells called __________
Meristems
What does it mean when we say plant growth is modular
made of repeated units
When does growth of a plant stop?
never
What doe meristem cells do?
Undergo mitosis to produce new cells
What happens after meristems grow?
The cells elongate
When do the CELLS stop growing?
Once they have completed maturing into different tissue
What does meristem tissue allow?
Allows plants to continuously grow and repair stems and roots but not leaves
Can leaves regenerate?
No
What kind of cells can meristem cells form?
Any
What does the fate of a new cell depend on?
The position in a plant, not which meristem it comes from
What are apical meristems and where are they located?
They extend the plant body outward in the process of primary growth, located in the buds and root tips
What does primary growth do?
Lengthens and causes branching of the plant body
Where does lengthening and branching occur in stems?
Surface buds
Where does lengthening occur in roots?
root tips, but branching growth originates internally from the pericycle
What is secondary growth?
An increase in a plant’s diameter
What does the extra diameter from secondary growth enable?
The extra diameter from secondary growth enables some gymnosperms and angiosperms plants to grow very tall. These plants are called
woody plants.
What results from secondary growth?
Two new types of meristems, vascular cambium and cork cambium
What does secondary growth produce?
Layers of cells that form wood and bark
What is bark composed of?
Both living tissue (phloem and cork cambium) and non-living cells (cork)
What is wood composed of?
Both living tissue (parenchyma in xylem rays) and non-living cells (secondary xylem)
What is the source of secondary xylem and phloem?
Vascular cambium
Where does secondary xylem and phloem form?
Secondary xylem forms towards the inside, and secondary phloem forms towards the outside
What happens when xylem cells are mature?
They are dead and form non-living wood
What does cork cambium do?
Renews and maintains an outer layer that protect the stem. It produces waxy, thick-walled cork cells, to the outside
What happens when cork cells are mature?
They are dead and accumulate in layers on non-living cork
What adds to the girth of woody plants?
secondary xylem
What do the older layers in secondary xylem in older stems eventually become?
Filled with plant resin
What is heartwood?
The inner layers of secondary xylem filled with plant resin
What can and cant heartwood do?
Strengthens the trunk, but it cannot transport water and minerals
What is sapwood?
The unclogged functioning outer layers of xylem
What can be determined by xylem rings?
The age and history of a tree
What happens to the phloem when xylem accumulate?
The phloem layers split and the spaces get filled with parenchyma cells
What happens to older phloem cells as xylem accumulates?
They get crushed against the cork layer
Why can’t you determine the age of a stem by counting phloem layers?
Phloem layers crack and get filled in, so it is not a reliable way to determine age
What happens in the cork cambium?
It is actively increasing in diameter, creating a protective layer
What is cork?
Cells produced by the cork cambium
What happens that requires new cork cambium?
he outer cork layers crack and peel by accumulating xylem
How can cork layers be used to determine tree species?
Cork layers can grow unevenly resulting in different bark growth patterns that are species specific
True or false: Old cork layers can be removed with no harm to the tree
True
What is girdling?
Peeling the entire bark off a tree
Can girdling kill a tree?
yes
What is bark made up of?
cortex and secondary phloem
What is wood made up of?
xylem
What do bark and wood share?
Vascular cambium
What does removing the bark from a tree do?
Removes the phloem layers with the cork, preventing any sugars from getting to the roots. It also damages the cambium, preventing any regrowth of cork or vascular tissue
Summarize what primary growth does
Lengthens and causes branching of the pant body
Summarize secondary growth
increases the width of stems and roots. Can occur in some angiosperms and gymnosperms, resulting in wood and bark
