4.1: Systems in Plants
pg. 125
Plants are multicellular organisms, with two distinguishing features;
they are green in colour and cannot move from place to place.
Plants are green because they have organelles called chloroplasts
that contain the pigment chlorophyll. This is the site of
photosynthesis. Plants have roots which allow them to transport
water and minerals from the soil to the leaves. Roots also anchor
the plant in one location.
The main features of a flowering plant are divided into two body
systems; shoot system and the root system.
Figure 1: A typical flowering plant has two body systems: the root system and the shoot
system.
Plants are autotrophs; this means they can make their own food
through a process called photosynthesis. They do not have to get
food from the environment. They do not have organs systems like
animals. However, plants do have to perform many of the same
functions as animals.
- Plants need to exchange gases with their surroundings,
- They require an internal transport system, to move water
and nutrients around their body,
- They must have a way to reproduce.
Hierarchy of Organization in the Plant Body
The plant has two body systems, shoot and root systems.
The Root system is made up of roots, either one or many,
depending on the type of plant.
The Shoot system may be made up of four parts, stem, leaf, flower
and fruit.
Plants are made up of a wide variety of specialized cells groups of
cells are called tissues. These tissues are group into, dermal,
vascular, and ground tissues.
Dermal Tissue – the tissues covering the outer surface of the plant.
Vascular Tissue – the tissues responsible for conducting materials
within the plant, (xylem and phloem)
Ground Tissue – all plants tissues other than those that make up
the dermal and vascular tissue systems.
The Root System
Root System – the system in a flowering plant, fern, or conifer that
anchors the plant absorbs water and minerals, and stores food.
The root system grows underground, and can spread out to cover a
large area.
Roots are also a useful supply of food, flavour, fibre, and natural
remedies.
The Shoot System
The shoot system has two functions; to conduct photosynthesis,
and produce flowers for reproduction. Flower plants have three
parts to their shoot systems; the leaf, the flower and the stem.
The Leaf
The leaf is the primary site for photosynthesis, there is a high
concentration of chloroplast in the cells that make up the leaf.
Sun light + Water + Carbon Dioxide → Glucose + Oxygen
The Flower
The Flower is a specialized structure for sexual reproduction. The
flower contains both the male (stamen) and female (pistil) parts.
Pollen grains from the male must fertilize the eggs found in the
female part. After pollination, seeds start to form, in specialized
structures called fruit.
Pollination is assisted by the wind or animals (Bees). They carry
the pollen grains to other plants to pollinate the female portions.
The Stem
The stem has many functions, support branches, leaves, and
flowers. Transport nutrients and water, through vascular tissues, to
other regions in the plant, such as; roots, leaves, flowers, and fruits.
Some stems are specialized for food storage, protection,
photosynthesis and reproduction.
Check Your Learning, questions 1 – 7, pg. 128
4.2: Plant Tissue Systems
pg. 129
There are three tissue systems, which included specialized cell
types, performing specific functions within the plant.
Cellular Differentiation
When the seed starts to grow the cells undergo mitosis very
quickly as the embryo develops. Eventually the cells start to
differentiate into specific tissues.
The growth areas in plants are found in the root tips and the shoots.
Trees also have an area just below the surface of the stem cells.
Plant growth occurs because undifferentiated cells are actively
growing and dividing in these regions. As these new cells mature,
they specialize and develop new features according to their
location and function.
Meristematic Cells
Meristematic Cells – an undifferentiated plant cell that can divide
and differentiate to form specialized cells
The meristem region of the onion root tip divide, differentiate into
specialized tissues in the roots. The same occurs in the stem’s
shoot regions.
Tissue System in Plants
The three major tissue systems are the dermal, ground, and
vascular. Each type if tissue produces its own type of specialized
cells.
Figure 3: General arrangement of plant tissues. The vascular tissues are shown in red, the
dermal tissues in green, and the ground tissues in light blue.
Dermal Tissue System
Epidermal tissue (epidermis) – is a thin layer of cells covering all
non-woody surfaces of the plant.
Periderm tissue – the tissue on the surface of the plant that
produces bark on stems and roots.
The dermal tissue forms the outermost layer of a plant. Dermal
tissue includes both the epidermal and periderm layers.
The cells of the dermal tissue are specialized to perform a variety
of functions. Epidermal root cells are responsible for absorbing
water and minerals from the soil. The dermal layer also produces a
waxy layer called the Cuticle. The cuticle helps waterproof the
plant and protects it.
Vascular Tissue System
Xylem – vascular tissue in plants that transports water and
dissolved minerals from the roots to the leaves and stems of the
plants
Phloem – vascular tissue in plants that transport dissolved food
materials and hormones throughout the plant.
Figure 6: (a) in xylem tissue, water carries dissolved minerals upward from the root to
the shoot through dead, hollow cells. (b) In phloem tissue, dissolved sugar and other
nutrients are moved around the plant through living cells.
Plants obtain water and minerals from the soil through their roots,
which needs to be transported through out the plant, especially to
the leaves.
Plants must also transport sugars and other chemicals, produced
during photosynthesis, to all parts of the plant.
Vascular tissue is responsible for the transport of water, minerals,
glucose and hormones throughout the plant.
Xylem is hollow tubes, with rigid walls, which allow water and
dissolved minerals to travel up the stems to the leaves and other
cells.
Phloem transports solutions of sugars, produced during
photosynthesis, and hormones to the cells of the plant. The sugar is
usually transport to storage areas in the stems and roots.
Ground Tissue
Ground tissue is the filler between the dermal and the vascular
tissues. Ground tissues perform a variety of functions; green parts
of plants where photosynthesis occurs, the roots where
carbohydrates are stored, and stems where storage occurs and
support.
Check Your Learning, questions 1 – 6, pg. 133
4.4: Tissues Working Together
pg. 136
The Shoot System in flowering plants conducts photosynthesis and
reproduces sexually; and consists of the leaf, the flower, and a
stem.
The leaf has one primary function, performing photosynthesis. The
tissue systems of the leaf must work together to perform this task.
Photosynthesis is the process that enables plants to create glucose
from water, carbon dioxide and sunlight energy.
Sunlight energy + water + carbon dioxide → glucose + oxygen
The glucose is then converted into complex sugars, carbohydrates.
These carbohydrates form starches, which are a source of chemical
energy, stored in the plant.
The glucose is used by all organisms to survive, including plants,
during a process of cellular respiration.
Glucose + oxygen → water + carbon dioxide + ATP
Absorbing Light
Palisade Mesophyll – a layer of tall, closely packed cells
containing chloroplasts, just below the upper surface of a leaf; a
type of ground tissue.
Spongy Mesophyll – a region of loosely packed cells containing
chloroplasts, in the middle of a leaf; a type of ground tissue.
Leaves are green and thin, which make them ideal for absorbing
sunlight energy. Broad leaves have a greater surface area for light
absorption, which increases the efficiency. The leaf is green
because of the pigment found in the chloroplast, chlorophyll.
There are two layers of tissues found in the leaves that perform
photosynthesis, the Palisade and Spongy mesophyll cells. The
palisade cells are the primary cells that perform photosynthesis;
they are closely compact together and found in the upper layer of
the leaf.
The spongy mesophyll, are located below the palisade layer, and
absorb light energy that passes beyond the palisade layer. These
cells are spaced apart creating gaps to allow gases to move around.
Figure 2: The specialized tissues and cells in a leaf.
Obtaining Carbon Dioxide
Cuticle – a layer of wax on the upper and lower surfaces of a leaf
that blocks the diffusion of water and gases.
Stomate (stomata) an opening in the surface of a leaf that allows
the exchange of gases.
Guard cell – one of a pair of special cells in the epidermis that
surround and control the opening and closing of each stomate.
For photosynthesis to occur carbon dioxide must enter the leaf and
oxygen is released. Gases are prevented from diffusing into the
leaf because of the cuticle layer, instead the gases enter and exit
through special openings called stomata. These opening are
controlled by guard cells. The stomata are primarily located on the
lower surface of the leaf, which helps reduce water loss.
Controlling Stomata
The stomata need to open to allow Carbon dioxide and oxygen to
be exchanged with the atmosphere, and photosynthesis to occur.
The stomata open when it is sunny, but will close if the if water
loss is great. The guard cells are responsible for opening or closing
the stomata. If there is not enough water, the guard cells will close
the stomata to prevent anymore water loss.
Obtaining Water
The leaf obtains water, vascular tissue (xylem), from the roots of
the plant. The roots and root hairs absorb water from the
surrounding soil, through osmosis.
Comparing Plant and Animal Systems
Both animals and plants cellular respire, therefore require oxygen
and glucose and produce carbon dioxide and water.
The movement of fluids, in both animal and plants, is similar. Both
have tissues responsible for the movement of materials throughout
the organism. Xylem and phloem of the plant is similar to the
arteries and veins in animal’s circulatory system.
Check Your Learning, questions 1 – 7, pg. 139
4.6: Plant Growth
pg. 143
Plant growth is totally different from animals. In animals growth
occurs throughout the body, in plants the growth only occurs in
certain parts of the plant. Animals will only grow to a certain size,
while plants continue to grow to be massive.
Plant Meristems
Apical meristem: are undifferentiated cells at the tips of plant roots
and shoots; cells that divide, enabling the plant to grow longer and
develop specialized tissues.
Lateral meristem: are undifferentiated cells under the bark in the
stems and roots of woody plants; cells that divide, enabling the
plant to grow wider and develop specialized tissues in the stem.
Figure 1: Meristem regions in a woody plant.
Figure 2: The only cell division in a root tales place in the apical meristem. Then the
cells elongate, differentiate into various kinds of specialized tissue, and mature.
Lateral Meristems
Trees are woody plants that grow in height and diameter. Lateral
meristems within their stems and roots which form two cylinders,
one inside the other, that run the full length of the shoots and roots.
Figure 4: In the roots and shoots lateral meristem differentiates into vascular tissue
(xylem and phloem) and epidermal tissue. Each year’s growth of new vascular tissue
forms a visible ring of ells.
Check Your Learning, questions 1 – 7, pg. 147