plants: cells, tissues, organs and organ systems

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Plants: Cells, Tissues, Organs and
Organ Systems
Before we get into plants....... The cell membrane of a cell is a barrier through which everything must pass on
its way into or out of the cell
Passage across the cell membrane occurs through a process of Diffusion the movement of molecules from areas of high concentration to areas of low concentration
Osmosis the diffusion of water across the cell membrane from areas of high concentration to areas of low concentration
The cell membrane is selectively permeable; not all materials can cross
Some materials are kept in or out while other more important materials (e.g. Oxygen and H2O) are allowed to move in and out of the cell
Cell Specialization and Differentiation
How do seeds change into seedlings and finally into adult plants? The answer lies in cell specialization – the process by which cells develop and mature to exhibit specific functions within a multi-cellular organism
Cell Differentiation is the stage of development of a living organism during which specialized cells form to perform different functions in the organism
Cells are specialized according to the set of proteins they contain; genes are responsible for the regulation and production of these proteins
All cells in an organism contain the same genes but not all the genes are turned on; the genes that are turned on in a particular cell will produce proteins that make the cell specialized giving it a particular role or function
Specialized Cells and Tissues in Plants
Meristimatic cells (Meristems) are undifferentiated cells that give rise to a specfic type of specialized cell these cells have the lifelong ability to become cells of new tissues and organs in a particular part of a plant
Groups of specialized cells form tissues – a cluster of similar cells that share the same specialized structure and function; the 3 major types of tissue in plants are; Dermal Tissue Ground Tissue Vascular Tissue
Several types of tissues combine to work together and perform a specific function in organs; the 4 major organs found in plants are; Leaves Stems Roots Flowers
You are responsible to know the name and function of;
The 3 types of tissues found in the body of the plant
The 4 major organ systems in the body of the plant
The Leaf Divided into 3 parts; Upper Leaf, Middle Leaf and Lower Leaf
The leaf’s most important job is to provide a large surface area where photosynthesis can take place
Be familiar with the name and function of the components of the leaf
The Lower Leaf and Gas Exchange
To allow gases (O2 and CO2) to move in and out of the plant, the leaf contains guard cells scattered across the lower surface
Guard cells change their shape to control the opening and closing of pores in the leaf which are called stomata or stoma for singular
Stomata are connected to the open spaces in the spongy parenchyma
The guard cells and stomata play a significant role in; Transpiration (the evaporation of water (H2O) from leaves) The exchange of carbon dioxide and oxygen (O2 exits and CO2 enter )
Chloroplasts Chloroplasts are found on the guard cells within the leaves of a plant
Function by trapping the sun’s light energy and combining it with carbon dioxide (CO2) and water to make glucose, a carbohydrate broken down in the mitochondria to provide energy for cell activity
The above process is known as photosynthesis
Chloroplasts can change their shape and location in a cell to increase the amount of light they capture
Chloroplasts contain little sacs called thylakoids arranged in stacks called granum which contain a light-trapping pigment known as chlorophyll; the part of the chloroplast where photosynthesis occurs
The Stem A plant’s stem has 2 major functions; physical support and transportation
of water, nutrients and sugar
The stem is made up of the Xylem and Phloem
Xylem Dead tubular cells with thick cell walls that form long hollow vessels or “pipes” through which water can flow
Xylem vessels are grouped with phloem vessels in vascular bundles
Phloem Living vertically stacked tubes that are pourous allowing water and minerals to be exchanged and transported between the phloem and neighbouring cells in the plant
The Roots Roots anchor a plant to the ground, allow
it take up water and minerals from the soil and act as a plant’s storage area
The root hairs are the main site of water and mineral absorption
The endodermis helps control the transport of minerals between the cortex and the vascular tissue
The pericycle is a layer of tissue surrounding the phloem and xylem
• The two major types of roots are taproots and fibrous roots you
should know the structure and function of each of these root types
The Flower The flower does not take part in the maintenance of the plant; it is responsible
for reproduction
The flower is made up of specialized leaves, one which is known as pollen which manufactures sperm and another type is responsible for manufacturing a set of eggs
Plants accomplish pollination with the assistance of the wind and small animals
Flowers attract these animals and insects to the plant through colours and scent
These organisms pick up the pollen from the male part of the flower and transfer this pollen to the female parts of the same or another plant of the same type setting the stage for fertilization
Plant Systems
A plants internal structure contains many interactions between various organs and tissues which perform specific functions These tissue and organ systems working together are known as a system which maintain a constant flow of fluids, nutrients and hormones throughout the plant
A plant has 2 major organ systems Root System consists of all the roots that lie below
the surface of the ground and is responsible for taking in water and minerals from the soil and transporting these substances to the shoot system
Shoot System consists of the remainder of the plant above the ground and is responsible for support the plant and performing photosynthesis and transportation of water minerals and sugar
Plant Systems Work Together The root and shoot system are connected by the flow of water and
nutrients through vascular bundles containing xylem and phloem
Xylem tissue moves water from the roots to the leaves, where this material is needed for photosynthesis
Phloem tissue moves the sugars produced by photosynthesis in the leaves to other parts of the plants; phloem cells utilize the plant’s energy stores to actively pump substance to where they are needed in the plant (e.g. Phloem tissue moves glucose from the leaves to the buds where it is utilized and to the roots where it is stored)
Note: Xylem tissue dies at maturity so it does not use any of the plant’s energy stores
Moving Water Through Systems Water is essential for any plants survival
Nutrients in the soil need to be dissolved in water in order to be
absorbed and move up the phloem in the form of sap
Water is also a critical component of photosynthesis in the leaf
Without sufficient water supply a plant would eventually die, however
too much water in the soil can have negative effects
Keeping water levels balanced and constantly moving through the plant is
vital This requires interactions from the root and shoot system
Moving Through the Roots
The roots helps plants absorb water and minerals from soil; Root hairs expand the roots total surface area water and nutrients are transported into the root through osmosis and diffusion
The nutrients and water move toward the xylem at the centre of the root and then pushed up and into the xylem vessels
The Push and Pull of Water Movement up the Xylem
1) Push From Root Pressure
Root Pressure occurs when transpiration (evaporation of water from
leaves) is low and when soil is moist as root cells bring minerals into the
xylem and phloem, the mineral concentration in these structures increase
The high concentration of minerals causes water to diffuse into the root
xylem by osmosis as water flows in, the root pressure builds in the
xylem which forces fluid up the xylem
2) Transpiration
Xylem tissue ends when it reaches the leaves; here liquid water turns into
water vapour in the middle of the leaf; this is the process of transpiration
Transpiration makes room for more water to come up from the xylem to
move into the leaves, pulling the water column up
Transpiration Root pressure is not sufficient to move water to the top of tall trees alone; Transpiration is the main factor which moves water up the xylem
Transpiration, along with some of water’s unique properties move water up the Xylem
Cohesion ability of water molecules to cling to each other holds the water in the xylem together
Adhesion tendency of water molecules to stick to the surfaces of the walls of the xylem prevents water from flowing back down the roots
The rate of transpiration is controlled by the amount of water vapour in the leaves when their is a lot of water vapour the guard cells open the stomata and water vapour moves out of the leaves when their is little to no water vapour the guard cells relax and close the stomata
Moving Nutrients Through Plants Photosynthesis produces the sugar glucose
Glucose is either used directly or is combined with other molecules to
produce other sugars like sucrose, the main sugar distributed to other
parts of the plant through the phloem
Sucrose that makes its way to the roots is chemically changed into starch
and stored when stored starch is needed by other plant organs, it
must be removed from storage and transported
Starch is not soluble in water, however sucrose is therefore starch is
converted back to sucrose, dissolved in water and is transported as sap
The Movement of Maple Sap In the spring, trees need to nourish the many buds that must divide and
grow to produce leaves the photosynthesize
Sap flows upward from the roots through the phloem of the maple trees in the spring which contains large amounts of sucrose that has been converted from starch
Sap moves through the phloem to where it is needed in the buds where leaves are growing