mod 2.1 - organisation of cells Flashcards
What are unicellular organisms?
First forms on Earth were unicellular organisms that arose more than 3.8 million years ago.
Unicellular organisms, such as the prokaryote Escherichia coli and the eukaryote Euglena, a single cell must carry out all functions, including obtaining nutrients, exchanging gases, removing waste and reproducing.
Unicellular organisms can live together in groups; however each cell is still capable of breaking away and living individually.
What are multicellular organisms?
A multicellular organism is like a community of cells that work cooperatively for the survival and reproduction of the organism.
All consist of eukaryotic cells.
There is a huge diversity of multicellular organisms, from simple mosses to complex flowering plants, birds and mammals.
For an organism to be considered multicellular, it must have multiple specialised cells that are responsible for specific functions (such as reproduction). And in addition, its cells must:
Have the same DNA (except for the reproductive cells).
Be connected and must communicate and cooperate to function as a single organism.
Be dependent on each other for survival.
What are colonial organisms?
This is a special form of a multicellular organism that consists of many individuals living together.
What are the two types of colonial organisms?
Facultative colonies and obligate colonies.
What are facultative colonies?
Are usually independent organisms that aggregate together to form complex social structures that increase the chance of survival. (eg: honey bees)
What are obligate colonies?
Consist of individuals called zooids that vary in form and carry out specific functions for the organism to survive.
Individuals in an obligate colony are dependent on one another for survival and reproduction and are sometimes physically connected.
eg: parasites, which need a host to complete part of a life cycle, or sea jellies, which are made up of individuals with specialised roles.
Prokaryotes are not multicellular organisms, however, come bacteria, such as cyanobacteria, grow in chains of cells; and others form aggregates or colonies of cells that behave in a coordinated fashion, such as species that form biofilms.
What are the advantages and disadvantages of multicellularity?
see notes.
What are the levels of organisation in multicellular organisms?
Depending on their complexity, multicellular organisms can be organised into the following levels to meet the needs of the entire organism: Organelles Specialised cells Tissues Organs Systems Organisms
What are organelles?
Cells vary in the number and type of organelles they have, based on the cell’s function.
eg: animal cells that require large energy reserves will contain more mitochondria than other cells. Plant cells that require additional water to maintain their shape may possess larger vacuoles than other plant cells. And chloroplasts, the organelles that carry out photosynthesis, are only found in plant cells that photosynthesise, such as leaf cells.
What are specialised cells?
Are cells that have a specific function.
All cells are adapted to perform different jobs in a multicellular organism, and have unique structural adaptations that enable them to carry out these functions.
Specialised cells are the building blocks of complex tissues and organs in multicellular organisms. [eg: root hair cells, which absorb and transport water; leaf palisade cells, which absorb light for photosynthesis; and leaf guard cells, which open and close to regulate gas exchange. In animals, specialised cells include myocytes (muscle cells), erythrocytes (red blood cells), epithelial cells and neurons]
What are tissues?
Specialised cells are organised into tissues.
A tissue is a group of similar cells working together to carry out specific functions in multicellular organisms.
As organisms become more complex, tissues alone may not be enough to carry out all the tasks required.
In these cases, tissues have evolved to group together in distinct structures called organs.
What are organs?
Consists of two or more tissues that work together to perform one or more specialised tasks.
eg: flowers, leaves and roots in plants; the heart, liver and brain in mammals.
What are systems?
A group of organs that work together to perform a vital task, such as the circulatory and respiratory system in humans.
What are organisms?
In a complex animal, systems work together and contribute to the successful functioning and reproduction of the whole organism.
What is the organisation of simple multicellular organisms?
Some multicellular organisms are organised only at the cellular level. (eg: sponges) These animals are considered tissue-less multicellular organisms, because their cells aren’t organised into functioning systems within the organism.
Give eg of simple multicellular organisms?
In sponges, the body is hollow and consists of two layers of eukaryotic cells separated by a jelly-like substance. The outer layer protects it and contains tiny pores where water and food can enter. The inner layer consists of several cell types, including collar cells and amoebocytes.
Sponges produce toxins that prevent predators from eating them, and powerful antibiotics that fight infections from bacteria.
Despite the simple organisation of these organisms, each of their different cell types found within them has a specialised function that contributes to tier survival and reproduction.
Give another eg of simple multicellular organisms?
Cnidarians (sea jellies and anemones) have specialised cells (cnidocytes or nematocysts) for defence and capturing prey. These cells are found along the tentacles and a thread is fired from the cnidocyte which wraps around and taps prey. Some species, such as sea jellies or anemones, have cnidocytes that contain toxins for stinging and paralysing prey.
What are vascular plants?
Plants that have specialised tissues → vascular tissues (xylem/phloem) for transporting water and nutrients.
What are non-vascular plants?
Such as algae and mosses don’t have vascular tissue or true organs; instead they have simplified tissues and absorb water directly through their cell walls, transporting it between cells via osmosis.
The absence of vascular tissue in non-vascular plants also limits their size, due to the lack of structural support and limited area over which they can transport water and nutrients.
What are angiosperms?
Flowering plants.
What are the higher levels of organisation?
Tissues, organs and systems.
What are some specialised cells in complex plants?
Some of the most important functions in vascular plants are involved in the transport of nutrients and water and acquiring energy via photosynthesis.
Many specialised cells are found within the vascular tissue of plants for these functions.
What are some tissues in complex plants?
The characteristic tissues in vascular plants are the vascular tissues, xylem and phloem.
What are organs in complex plants?
Roots, leaves, stems, flowers and fruits.
What are the two systems in vascular plants and what are they?
The root system: usually underground, the root system supports the structure of the plant and absorbs water and nutrients (mineral ions) from the soil.
The shoot system: made up of two parts:
The non-reproductive (vegative) parts of the plant, such as leaves and stems.
The reproductive parts, such as flowers and fruits.
What are some specialised cells in complex animals?
The roles of these cells are critical to the functioning of the organism.
eg: nerve cells play essential roles in processing and transmitting signals throughout the body.
What are some tissues in complex animals?
Tissues contain specialised cells working together to complete a specific function.
Cells don’t need to be identical to be considered a tissue; they just need to be working together to carry out a certain function. (eg: blood is a tissue that consists of red blood cells, white blood cells and platelets that all work together)
What are the four main types of tissues in complex animals?
Muscle tissue
Nerve tissue
Connective tissue
Epithelial tissue
