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Exam 2 Study Guide
- Course
- BIO 1A
- Institution
- Las Positas College
This is an exam study guide for botany exam 2
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Topic 04 – Roots Part 2Key terms
Rhizosphere: the region of soil in the vicinity of plant roots in which the chemistry and
microbiology are influenced by their growth, respiration, and nutrient exchange.
Border cells: cells that disperse into suspension within seconds when root tips are placed into
water
Taproot: a straight tapering root growing vertically downward and forming the center from which
subsidiary rootlets spring
Fine root: typically primary roots <2 mm diameter that has the function of water and nutrient
uptake. They are often heavily branched and support mycorrhizas
Root hair: each of a large number of elongated microscopic outgrowths from the outer layer of
cells in a root, absorbing moisture and nutrients from the soil
Epidermis: epidermis is a single layer of cells that covers the leaves, flowers, roots, and stems
of plants. It forms a boundary between the plant and the external environment.
Cortex: allows water flow between the cells until it reaches endodermis
Endodermis: endodermal layer in a plant, almost always in the root, regulates the water and
other substances that get into the plant. The endodermis is a single layer of cells that border the
cortex of a root. The whole system in which the endodermis functions allows the roots to select
what gets into the vascular core
Vascular tissue: the tissue in higher plants that constitutes the vascular system, consisting of
phloem and xylem, by which water and nutrients are conducted throughout the plant.
Casparian strip: a strip of waxy material that blocks water flow between cells and force water to
cross a plasma membrane of endodermal before entering the vascular cylinder
Mycorrhizae: a group of fungi forms a mutualistic relationship with plant roots; increases
surface area of soil that plant is exploring; more than 80% of flowering plants and all
gymnosperms, helps absorb nutrients from the soil through thin filaments called hyphae;
mycorrhizae helps plant absorb phosphorus, nitrogen, and water from the soil and the plant
provides sugar to the fungi.
Auxin: hormone promotes root growth
Questions fix questions
1. Summarize the primary functions of roots. Give an example of each function. (Hint: we
discussed 7 primary functions of roots but you can ignore absorption and anchorage because
we already covered those on Exam #1)
- 1. *Anchorage*
- 2. *Absorption *
- 3. *Storage*: many roots are storage organs; food made in leaves is transported to the
root for storage; some food is used to maintain the roots and can be transferred back to
shoot via the phloem; examples seeds, fruit, flowers, and leaves.
, - 4. *Conduction*: (movement); roots can move sugar, hormones, secondary metabolites
(molecules only made in part of the plant that is not part of regular metabolism ex.
Alkaloids, terpenoids, phenolics)
- 5. *Clonal Regeneration*: roots of some eudicots can produce buds that make new
shoots (ex quaking aspen); Pando: one tree with root system 80,000 years old.
- 6. Redistribution of Water: hydraulic lift helps plant move water from groundwater to
soil surface at nights; due to the water potential LOW to HIGH
- 7.*Rhizosphere*: volume of soil around living plant roots; plants secrete into
rhizosphere; as the root grows the longer the root cap pushes down to the soil and the
root cap secretes mucus to easily move through the soil; the border cells secrete
mucilage to lubricate the root and bits of the root cap will fall off and change their gene
expression when detached from the root
- Soil Water: distribution of water in the soil includes surface water (1-3 feet deep), dry
area (4-6 feet deep), and deep water (7-8 feet deep); not evenly distributed, more at the
surface and deep (less in the middle); water in soil occurs in thin films around small
pieces of soil; root hairs can fit in and access these films; increases surface area.
- Application: tissue culture can produce genetically identical plants; or give hormones
such as auxin (root growth) and cytokinins (shoot growth); in horticulture, you can make
a cutting, break off a piece to make a new plant and add auxin to the piece to grow new
roots.
2. Why do some plants store carbon in their roots? Within one season of growth (i.e. Spring,
Summer, Fall, Winter), when would a plant be likely to access carbon reserved stored in the
root? Plants store carbon in their roots. Carbohydrate reserves (stored as starch), which have
been stored in the stems, roots, rhizomes, and stolons during the winter, are used by the plant
to provide energy and carbon to begin spring growth.
3. Describe how root hairs and mycorrhizae increase the absorption of water and/or nutrients
from the soil. The root hairs are where most water absorption happens. They are long and so
they can penetrate between soil particles, and prevent harmful bacterial organisms from
entering the plant through the xylem vessels. They have a large surface area for absorption of
water. Increasing root surface area aids plants to be more efficient in absorbing nutrients and
establishing relationships with microbes. The Mycorrhizae increases the surface area and
absorption.
4. Describe one example we discussed in the lecture of clonal regeneration of plant shoots
from roots.
5. Describe the functions of border cells of the root cap:
As the root grows the longer the root cap pushes down to the soil and the root cap secretes
mucus to easily move through the soil; the border cells secrete mucilage to lubricate the root
and bits of the root cap will fall off and change their gene expression when detached from the
, root; these can stay alive for weeks and could have the function of attracting positive bacteria,
repulsing bad bacteria, or is the majority of carbon-rich compounds in the soil and feed the soil
food web
6. Trace the movement of an ion from the soil to the center of a root, listing all tissues through
which the ion must pass. Describe the function of each tissue.
7. Explain the role of the endodermis in regulating the movement of substances into and out of
the root’s vascular cylinder. Endodermal cells have a strip of waxy material, the Casparian strip
that blocks water blow between cells and forces water to cross a plasma membrane of
endodermal cells before entering the vascular cylinder.
8. Review the material covered on the mycorrhizae handout we completed in lecture.
Topic 05 Mineral Nutrition
Key Terms:
Macronutrient: nutrients needed in large quantities
Micronutrient: nutrients needed in small quantities
Weathering: physical breakdown of minerals and rocks
Chlorosis: abnormal reduction or loss of the normal green coloration of leaves of plants
Mineralization: organic compounds broken down by soil organisms (microorganisms) (some
macro, like worms)
nutrient deficiency: symptoms depend on the role of nutrients and how easily nutrient is
transported (mobility); plants can move some nutrients from old leaves to younger leaves;
phloem mobile: old leaves symptomatic (Mg, P, K, N); phloem immobile: new leaves
symptomatic (B, Fe, Ca)
Ammonium: plants use for nitrogen uptake; Converted quickly into organic compounds (ex
amino acids). Feed into biochemical pathways that lead to amino acids
Nitrate: an organic compound; converted to NH4 to be incorporated into organic compounds.
Requires energy
Rhizobium: a genus of bacteria, nitrogen-fixing bacteria that fix nitrogen gas and turns into
ammonium; wrapped by root hairs and makes an infection threat that goes to the cortex and
forms nodule, inside the nodule N2 is converted to NH4
Nodule: a place where N2 is converted to NH4; forms when rhizobia invade plant, inside nodule
N2 is fixed in NH4 & converted to organic compounds; small swelling of cells in the body
N-fixation: the chemical processes by which atmospheric nitrogen is assimilated into organic
compounds, especially by certain microorganisms as part of the nitrogen cycle
Nitrogenase: an enzyme that makes nitrogen; fix (captures.obtains) N2 gas, requires a lot of
energy and O2 (cellular respiration)
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