Biology - Cell Specialization, Animal Cells, Plant Cells

Exploring Cell Specialization

• Unicellular organisms are living creatures made up of only one cell

• All the functions required by the organism are carried out within that cell

• Multicellular organisms, on the other hand, are much more complex and require many different types of specialized cells to carry out various functions

Cell Specialization

• If multiple cells with the same functions are joined together, the structure is called a tissue

• If multiple tissues work together to perform a specific task, they are referred to as an organ

• If multiple organs work together to perform a specific task (respiration, digestion, reproduction), they are referred to as an organ system

• Multiple organ systems are integrated into the overall function of an organism, or complete life form

Types of Specialized Cell 

• Plants and animals have their own unique types of specialized cells

• For example, animals have cells that are specialized for contracting (heart and muscle cells), digesting (mucosal and gland cells), structure (bone cells), communication (brain cells), transport (blood cells), as well as many more

Cell Specialization 

• Having different structures than animals, plants also have cells specialized for their needs

  • Plants have cells responsible for growth called meristematic cells, as well as cells responsible for transporting water and sugars

• Plants also need cells to protect the surface of stems and leaves, as well as cells within their leaves (mesophyll cells) that are responsible for turning light into food in the process called photosynthesis

• Since different types of cells have different functions, they contain different types of organelles 

• Cells in your pancreas are responsible for producing digestive enzymes, enzymes are made from protein, pancreatic cells contain large numbers of the organelles needed for protein production like ribosomes, endoplasmic reticulum, and Golgi apparatus

• Similarly, heart and muscle cells require large numbers of mitochondria to make the energy needed to keep the heart beating and move the animal around

• The shape of a cell is dictated by its function and the conditions under which it works

• For a cell to specialize, it may have to change shape, lose organelles (including the nucleus), or even shed little pieces of itself

Investigating Animal Cells 

Blood Cells

• Blood cells play important roles in both the immune system and the circulatory system

• Even though blood travels in a liquid form through veins, arteries, and capillaries, it is classified as tissue because it is a collection of different cells performing a set of particular tasks

• Blood is composed of two components: plasma and cells

• Making up the bulk of blood, plasma

  • Is a solution of water, dissolved gases, proteins, sugars, vitamins, minerals, and waste products

• 3 main types of blood cells

  • Red blood cells (erythrocytes)

  • White blood cells (leukocytes and lymphocytes)

  • Platelets

Red Blood Cells

• Red blood cells specialize in transporting oxygen throughout the body, they have a flattened, disk-shaped appearance

• This shape increases their surface area and allows them to travel within tiny vessels

• To maximize their effectiveness, red blood cells are missing most organelles, including a nucleus

  • Instead, they are packed full of oxygen-binding proteins known as hemoglobin

White Blood Cells 

• White blood cells are involved in the immune system

• All white blood cells contain nuclei, which makes them easy to distinguish from red blood cells

• The presence of a nucleus allows white blood cells to alter their function as needed to protect the body from different types of foreign invaders

• There are two types of white blood cells: 

• Leukocytes 

  • Leukocytes are large opaque blood cells that can either engulf (swallow) invading microorganisms or produce antibodies to fight off infection

• Lymphocytes.

  • Lymphocytes are white blood cells that are released in response to foreign invasion, they are designed to identify and mark as “non-self” any foreign cell in the blood, and release antibodies or other forms of defence to destroy the invader

Platelets 

• The final type of blood cell, the 

• Megakaryocyte (stays in the bone marrow)

  • Manufacture and shed millions of little pieces of themselves into the blood, these pieces of cell, called platelets, help the blood clot to seal up cuts and wounds

Nerve Cells

• The nervous system is the most important system in the entire human body

• It is responsible for responding to changes in the internal and external environment, the entire nervous system is an integrated network of nerves

• A nerve is a tissue made up of a bundle of specialized cells called neurons.

There are three types of neurons found within the human body:

• Sensory neurons

• Motor neurons 

• Interneurons 

Neurons 

• Sensory neurons receive the stimulus and send impulses to the brain

• Motor neurons carry impulses from the brain to muscles or glands

• Interneurons, found only within the brain and spinal cord, help coordinate the appropriate response and typically link the sensory and motor neurons

• Axon 

  • The long, thin part of a neuron

  • The signal generated in the main body of the neuron travels down the axon where it gets picked up by another neuron

• The smaller branching extensions are called dendrites, and this is where the neuron receives signals

• Most neurons have a similar structure; however, interneurons typically do not have dendrites

• A neuron uses electrochemical messages to communicate with other neurons

• These messages are transmitted by both electrical and chemical processes

• Dendrites receive the signals at connections called synapses. If the cell decides to respond, it sends an electrochemical impulse along its axon to the next neuron

• This electrochemical message is passed from neuron to neuron at lightning speed

Muscle cells 

• Muscle cells are another type of specialized cell that play an important role in the overall function of animals

• Used to move the body, muscle cells are often required to generate large amounts of force

• They contain many mitochondria to provide the necessary energy

• There are three different types of muscle cells

  • Cardiac muscle cells

  • Skeletal muscle cells

  • Smooth muscle cells

Skin Cells

• Skin is the largest organ of the human body, covering its entire surface

• It is called an organ because it is composed of multiple types of tissues

  • Dermal tissue (epidermis, dermis, hypodermis)

  • Glandular tissue (sweat glands, sebaceous glands)

  • Nervous tissue

• The main function of the skin is protection

• Skin cells are typically flat and thin with a brick or honeycomb shape that allows them to fit closely together to form a continuous protective layer

Bone Cells

• Bone cells are specialized to give the organism structure and support

• They combine in tissue layers to form bones

• Without bones, you would resemble a limp bag of jelly

• Bone cells are typically thick, they surround themselves with a thick mineral and protein coating that gives them their strength

There are three different types of bone cells:

• Osteoclasts

  • Large cells that contain more than one nucleus

  • Responsible for dissolving bone

• Osteoblasts

  • Contain only one nucleus and are found on the surface of the bone

  • They are responsible for forming new bones and often work in teams

• Osteocytes

  • Inside the bone that sense pressures or cracks in the bone, directing osteoclasts and osteoblasts to where they need to dissolve or repair bone

Reproductive Cells

• Reproductive cells are unique cells found in the testicles of males and the ovaries of females

• These cells undergo the specialized division process known as meiosis

• In both (males and females), meiosis results in four cells being produced from one

• In males, all four of these cells develop into functioning sperm cells

• In females, only one of these cells goes on to become an egg

• A human egg cell (called an ovum) is a large circular structure that contains a haploid nucleus with only 23 chromosomes (half the normal number in a human cell)

• One of the largest cells in the human body, the ovum is typically visible to the naked eye

• A human ovum measures between 100 and 200 µm (micrometres) in diameter

• The sperm cell is also a haploid cell, approximately 100 000 times smaller than an egg cell and consists of a head, body, and tail

• The Head is made up primarily of the nucleus

• This cell contains very little cytoplasm, which is shed during sperm maturation in order to decrease the weight and increase the speed of the sperm cell

• The body of the sperm contains many mitochondria used to provide fuel for the long journey in search of an egg

• Sperm cells are designed to do one thing— deliver genetic material to an egg as fast as they can

Understanding Plant Cells

Plant Cells

• Like animals, plants also have different types of cells

• These cells carry out specialized functions which allow the organism to grow and carry out its day-to-day activities

• There are many different kinds of specialized cells in plants and they can be grouped into the four most common types of tissues

How Cell Become Specialized

• You’ve encountered examples of specialized cells in animals and plants

• The initial unspecialized cell of an organism is referred to as a totipotent cell

  • This is a cell capable of expressing all its genes and can become any cell in the body, including other embryonic cells

• This initial unspecialized cell can then go through a process known as differentiation in order to become a specialized cell

• During the differentiation process, only portions of the total genetic information are expressed within each cell type

• In humans, the fertilized egg is totipotent until the eight-cell stage, at which point the cells begin to specialize

• Most plant cells retain totipotency even after becoming specialized

• This initial unspecialized cell is commonly referred to as a stem cell

Stem Cells and Ethical Concerns 

Stem Cells

• Stem cells are unspecialized cells that can continuously undergo the process of cell division without differentiating

• Though they cannot perform any specialized functions, stem cells give rise to cells that do develop specialized functions

Embryonic Stem Cells

• Embryonic stem cells are derived from the inner mass of the blastocyst stage of embryonic development

• A blastocyst is a 3 – 5 day-old embryo composed of two distinct cell types: cells that become the placenta and an inner mass of stem cells.

• Embryonic stem cells are pluripotent, which means they can become all cell types of the body except other embryonic cells; adult stem cells are generally limited to differentiating into different cell types of their tissue of origin

Adult Stem Cells

• Adult stem cells are rare and do not appear to have the same capacity or potential to differentiate as embryonic stem cells

• This would mean that adult stem cells are unipotent (can develop into only one cell type) rather than pluripotent

• Though rare, adult stem cells have been found in many different tissues such as the brain, bone marrow, skin, liver, skeletal muscle, and peripheral blood vessels