Cycling of Matter in Living Systems

Life from Life• -Spontaneous generation or

abiogenesis –Aristotle - living organisms arose spontaneously from nonliving matter was believed for 2000 years.

• - Francesco Redi (1626-1697) tested this theory with experiments – disproved abiogenesis

• - With the discovery of microorganisms abiogenesis was once again accepted.

Life from Life (continued)

• - Louis Pasteur (1822-1895) developed a swan-neck flask and through experiments disproved abiogenesis once and for all.

• -  Biogenesis – the theory that living organisms could only come from other living organisms Rudolf Virchow (1821-1902)

Developing the Cell Theory• - Robert Hooke (1635-1703)

looking at cork cells under a microscope coined the term ‘cells’

• Antony van Leeuwenhoek (1632-1723) first person to describe single celled organisms

- Theodor Schwann (1810-1882) studying animal cells and Matthias Schleiden (1804-1881)

The Cell Theory

• 1. All organisms are composed of one or more cells

• 2. The cell is the smallest functional unit of life

• 3. All cells are produced from other cells

• Work Page 265 Questions 1- 5

Cells and Technology

• - Simple microscopes used only one lens and were used early in science

• Electron microscopes use a beam of electrons instead of light and can magnify up to 1.2 million times

• - Compound Light microscopes first designed by Zacharias Janssen (1580-1638) had two lens and can magnify to 2000x

Cells and Technology continued

• Transmission electron microscope (TEM) gives a two dimensional image

Scanning electron microscope (SEM) sweeps a beam of electrons over the surface to create a three dimensional image

Cells and Technology continued• - Confocal laser scanning microscope

(CLSM) is used on thicker specimens, a laser beam is used to collect images on different planes and a computer puts the images together

• - Scanning Tunnelling microscope (STM) has greater magnifying power and is used to view things like DNA

A Molecular World

• - the genetic information in a cell is contained in the DNA molecules

• - DNA subunits consist of 4 bases• o   Adenine – A• o   Cytosine – C• o   Guanine – G• o   Thymine – T

A Molecular World (continued)• -The order of these bases are different

in every gene• Gene sequencing involves mapping the

order of the gene’s bases • - Human Genome Project (HGP) was an

international project to sequence all 30 000 to 40 000 human genes

• -  One of the ways researchers learn more about cancer causing genes is to determine their sequences

•Why are viruses and prions not considered living or a functional unit of life?

Culturing Cells

• Cell culturing is a valuable technique in cancer and cell research

• Isolated cells are placed in test tubes or petri dishes and supplied with all the nutrients they need for growth

Culturing Cells (continued)

• -The generations of cells that result are called cell lines

-Stem cells are cells that can divide to produce all other types of specialized cells. Most of the cells in a one week old embryo are stem cells. Most adult stem cells are in bone marrow, where new blood cells are produced

Work Page 276

Cell Membrane

• -  composed of a double layer of phospholipids – bilayer

• -   proteins and other molecules are embedded between and attached to the phospholipids

• -   the phospholipid has a head and a tail

• the head end is hydrophilic – ‘water-loving’

Cell Membrane (continued)• -  the tail end is hydrophobic –

‘water-fearing’ (do not dissolve readily in water)

• -  the two tail ends point to the middle – shielded from the water

• -  the heads point toward the water• -  the embedded proteins move

substances across the membrane and carry out chemical reactions

Cell Membrane (continued)•  some proteins may act as attachment

sites for messenger molecules - hormones

• the molecules that make up membranes are thought to be in constant motion – fluid-mosaic model

• carbohydrates – sugars attached to the membranes outer surface are involved with cell-to-cell communication

• are thin flexible and semi-permeable

Transport Across Cell Membranes • Brownian motion • particles are in constant motion• the motion is random• movement is always in a straight line • Passive Transport• molecules move without using energy• 3 types:

Transport Across Cell Membranes (continued)• 1.  Diffusion – net movement of molecules

from an area of high concentration to an area of lower concentration

• o   diffusion may occur across cell membranes• o   ends when an equilibrium occurs.• o   occurs faster the higher the temperature• o   always moves with the concentration

gradient, faster the greater the difference in concentration

• oxygen and carbon dioxide easily diffuse through cell membranes

Transport Across Cell Membranes (continued)• 1.  Osmosis• - is the diffusion of water from a higher

concentration to a lower concentration through a cell membrane

• o   hypotonic solutions lose water- they have more water and less solute than surrounding solution

• o   hypertonic solutions gain water – they have less water and more solute than the surrounding solution

• isotonic solutions are at equilibrium with their surroundings

Transport Across Cell Membranes (continued)• 1.  Facilitated Diffusion• o   glucose, ions and other substances too

big to diffuse through the cell membrane must have a way to get into the cells

• o   transport proteins are membrane proteins that help move molecules across the membrane

• o   are highly specific – only recognize certain molecules

• always occurs with the diffusion gradient

Transport Across Cell Membranes (continued)

• Active Transport • requires energy• may move molecules against the

concentration gradient• moves larger molecules

Transport Across Cell Membranes (continued)• Endocytosis• process that moves substances into a cell

that cannot be moved by other methods•  the cell membrane folds in forming a

pocket enclosing the molecule• this pinches off as a vacuole or vesicle• phagocytosis – when cell ‘eat’ large

particles, eg amoeba eating or white blood cells engulfing bacteria

Transport Across Cell Membranes (continued)

• pinocytosis –when cells ‘drink’ taking in droplets of fluid

• membrane proteins assist in this process – receptor-mediated endocytosis – eg cholesterol

 

Transport Across Cell Membranes (continued)• Exocytosis • allows the materials stored in

vesicles to exit the cell• opposite to endocytosis• very important to cells that

specialize in the secretion of cell products – hormones and enzymes

Plant Cells

• cells in the leaves of plants are designed to carry out different functions

• the main purpose is photosynthesis –during which energy from sunlight, carbon dioxide from the air and water from the soil are combined to make glucose

• glucose is important energy source for both plants and animals

Cellular Organization

• multicellular organisms have:• 1.    a larger size• 2.    a variety of specialized cells• 3.    an ability to thrive in a broader range

of environments• all of these demand organization• within a cell different functions are

preformed by organelles• groups of specialized cells are called

tissues

Cellular Organization (continued)

• groups of tissues that work together for one purpose are called organs

• organs working together form organ systems and many organ systems create an organism

Gas Exchange in Plants

• the stomata in surface cells of the leaves allow gas exchange to occur

• carbon dioxide, oxygen and water move in and out by diffusion

• these gases then circulate to other cells through the spaces in the spongy layer

Gas Exchange in Plants (continued)• in woody plants lens shaped openings

perforate the bark allowing direct gas exchange between the environment and the living cells just under the bark

• during cellular respiration plant cells consume oxygen and produce carbon dioxide and water

• during photosynthesis plants consume carbon dioxide and water and produce oxygen as waste

Water Loss by Plants

• transpiration is the evaporation of water from the leaves of plants

• water diffuses out of the stomata• guard cells can change their

shape to stop the loss of water on hot days thus preventing the plants from dying due to dehydration

Water Loss by Plants (continued)

• water moves in and out of the guard cells by osmosis

• when water moves in the cells swell due to increased pressure – turgor pressure

• the swollen guard cells change shape opening the stomata

Water Loss by Plants (continued)

• when water decreases in the guard cells the cells deflate and the stomata closes

  - stomata open during the day and close at night

- in desert plants the stomata only open at night

Water Transport in Plants • Vascular plants have a system of

vessels that transport water, minerals and sugars throughout the plant.

• Xylem and phloem are the specialized tissues that make up the transport system

• Xylem tissue transports water and minerals from the soil to the leaves

Water Transport in Plants (continued)

• In mature plants most xylem cells are dead

• They form hollow tubes consisting only of cell walls

• The cells are connected end to end – xylem vessels

Water Transport in Plants (continued)

• Phloem cells transport the sugars produced during photosynthesis from the leaves to all parts of the plant

• Phloem vessels are living cells

Water

• cohesion is the tendency for water molecules to stick together

• this helps explain water moving upward in xylem vessels

• adhesion is the tendency of water molecules to stick to other surfaces – the clinging of xylem sap to the xylem walls helps to prevent the sap from falling back down to the roots

Water (continued)

• root pressure is the turgor pressure inside to root xylem

• this pressure only accounts the movement of water a few meters up a plant

• transpiration from the leaves pulls the water up

Sugars

• sugars produced by photosynthesis in the palisade and spongy cell provide energy for the whole plant

• phloem vessels transport the sugars throughout the plant

Plant Control Systems

 • 1.       Phototropism• the growth of a plant towards light is

called phototropism• this maximizes the amount of light

absorbed by plants• more lights more photosynthesis• the chemicals found to cause plants to

grow toward the light are auxins produced in the growing tips of some plants

Plant Control Systems (continued)•  • 2.       Gravitropism• is a plant growth response to the force of

gravity• plant stems grow away from the pull of

gravity – negative gravitropism• roots show positive gravitropism• auxins also explain the growth of the

plant in gravitropism

Plant Control Systems (continued)

• 3.    Nastic Response• response by plants to touch• eg Venus Fly Trap, Mimosa