BIOL111 Lecture 6
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In which group of plants did microphylls first appear?
Does the sporophyte of the gametophyte better protect against harmful mutations?
In which group of plants did stomata evolve first?
Which of the following groups of plants lacks motile sperms?
4. advanced algae
What are the 2 major groups of angiosperms?
dicots and monocots
what are the major defining features of monocots?
- fibrous root
- sheath leaf base
- parallel leaf venation
what are the major defining features of dicots?
- tap roots
- petiole leaf base
- reticulate leaf venation
What is the modular structure of stems?
- Structural unit of stem and root is called a phytomere
- In stem, one phytomere includes:
- 1. an internode
- 2. the leaf subtended at the upper end of the internode
- 3. the axillary bud in the axil of that leaf
What can a section of the main root along with a subtended root branch be considered?
a phytomer or a structural root module
What is unique about the angiosperm plant body unline animals?
- Has permanent embryonic regions or meristems
- The cells in these regions retain the capacity to divide throughout the life of the plant which may be thousands of years
What are apical meristems?
- Indeterminate or permanent
- -shoot apical meristem (SAM)
- -root apical meristem (RAM)
- The activity of apical meristems results in primary growth and increase the length of the shoot-root axis and the height of the plant
What is the lateral meristem?
- Indeterminate or permanent
- Cambium: produces xylem towards the inside and phloem towards the outside, increasing the diameter of the plant
What are temporary meristems?
Produce organs with finite size, such as leaf and flower parts. They lose ther meristematic character when the organ reaches full size (leaf, flower, etc)
Where are the permanent meristems located in higher plants?
- the terminal bud contains a shoot apical meristem
- in woody plants the vascular cambium and the cork cambium thicken the stem and root (lateral meristems)
- root apical meristem located on the root cap
How can you tell the difference between simple and compound leaves?
- simple - single blade; means one stem has one big leaf (like a maple leaf)
- compound - consist of leaflets arranged along a central axis (like most plants)
- doubly compound - further division of the axis (like a fern frond)
What are stipules?
- Little pointy things around leaf edge
- may be modified into tendrils or spines
Which 2 structures of a leaf can be modified into tendrils?
- Terminal leaflets
What is phyllotaxy?
patterns of leaf arrangement
Describe spiral phyllotaxy
leaves grow from stem in spiral pattern all the way around
Describe alternate phyllotaxy
alternate from side to side, leaves originate from their own spot
Describe distichous phyllotaxy
leaves on opposite sides of stem, grow flat, leaves originate from same spot on stem
Describe decussate phyllotaxy
in 3D space it is both alternate and distichous
Describe whorled phyllotaxy
4 leaves on all 4 sides of stem in 3D space
what is the shape of a monocot leaf?
consists of leaf sheath, leaf blade, and sometimes ligules and auricles
how are vascular bundles arranged in a cross-section of the stem in dicots?
in a ring
how are vascular bundles arranged in a cross-section of the stem in monocots?
what is the cambial ring?
- In dicots, cambium of adjacent vascular bundles gets joined forming the cambial ring
- The cell division activity of the cambial ring forms secondary xylem towards the inside secondary phloem towards outside, constituting secondary growth
What gives rise to concentric annual rings?
- Increase in dicot stem diameter by secondary growth
- Within an annual ring, cells formed during wet season are larger than cells formed during drier season. Thus an examination of annual rings in trees cross-sections can tell us abotu past climate
What is cork cambium?
- A lateral meristem
- Sometimes produced in the outer part of the bark and gives rise to cork
What is the periderm?
cork cambium and the tissues (cork and phelloderm) it produces are called periderm
What is a lenticel?
The cork is suberized to a water-impermeable layer. However the underlying cell layers still need to breathe. Thus outer layer of the corky layer is disrupted and forms a lenticel.
Memorize this picture for leaf structure and function:
What is RAM?
- root apical meristem
- covered by root cap the cells of which continuously slough off
How do cells in the root cap know which way to grow?
Cells at the center of the root cap sense gravity
Is there any part of the root that is dormant?
Yes, a few cells at the center of RAM constitute the quiescent center
Where are the cell growth centers in RAM?
There is a zone of cell division just behind the RAM followed by a zone of cell elongation which is followed y zone of cell maturation and specialization
What is the purpose of root hair?
- Present in the zone of maturation
- increase the surface area for absorption
Where do lateral branches arise from?
- Arise from pericycle, located deep inside the main root
- very difficult to break
Where do shoot branches arise from?
- Arise from the cortex, superficial layer
- very easy to break
Leaf modification - pitcher
- Leaf blade modified into a pitcher
- Makes carniverous plant
What is the typical flower structure?
- Pentamerous (mostly dicot) and trimerous (mostly monocot) flowers (petals)
- Top part of the peduncle/stalk of the flower is called thalamus
- Stamen = filament + anther
- Carpel = ovary + style + stigma
- Flower may have one or several carpels fused together
- You can cut a cross-section of a fruit and see how many carpels it has
All flower parts are modified _______.
Why is the stem radial in cross-section fortified by vascular system?
Radial symmetry is optimal in providing strength against lateral swaying stresses. It has bark/cork on outer surface to protect against pathogens
Why are the plant roots underground?
- Not subjected to wind pressures
- Although radial in cross-section their mechanical strength is located along the center of the cylinder
Why are leaves flat?
Intercepting maximum light for which a flat surface is optimal. Thus leaves are flat, bilaterally symmetrical with chlorophyll-containing cells concentrating on the upper part of the leaf interior
Why do monocot leaves nearly vertical?
Have no distinction of upper and lower parts of the leaf. Both sides intercept light
What are flower parts modified forms of?
Appropriately modified leaves to perform reproductive function
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