Participating in the Tree of Life series: Water and Light

This post is number 3 in a multi-part series on the Tree of Life.  This post addresses water and light in the life of plants, and how this is relevant to the Tree of Life message.  Here is a link to the first post, which explains the purpose of this series, and the second post.

Water and life

Water is absolutely essential to all life forms.  There is no life without water.  Why do we send space probes looking for water on Mars?  There’s no hope of finding life without water. 

Let’s take a look at the Gospel of John, 7:37-39

On the last and greatest day of the festival, Jesus stood and said in a loud voice, “Let anyone who is thirsty come to me and drink.  Whoever believes in me, as Scripture has said, rivers of living water will flow from within them.” By this he meant the Spirit, whom those who believed in him were later to receive. Up to that time the Spirit had not been given, since Jesus had not yet been glorified.

In the Bible, water symbolizes the Holy Spirit, and just as physical life depends on water, so does spiritual life depend on spiritual water.  In John 6:63, after Jesus feeds the 5000, and walks on water, He is teaching a crowd, and says, 

The Spirit gives life; the flesh counts for nothing. The words I have spoken to you—they are full of the Spirit and life.

Let’s revisit the Bible passage which anchors this study, Revelation 22: 1-3: 

Then the angel showed me the river of the water of life, as clear as crystal, flowing from the throne of God and of the Lamb down the middle of the great street of the city. On each side of the river stood the tree of life, bearing twelve crops of fruit, yielding its fruit every month. And the leaves of the tree are for the healing of the nations.  No longer will there be any curse.

It’s clear the river of the water of life indicates the Holy Spirit, and it flows by the tree of life which is oddly positioned on each side of the river (we’ll get to that in another post).  It’s clear that the tree of life is sustained by the river of the water of life.  Let’s look more closely at the interaction of water and a tree, from a biological perspective, so that we can better understand aspects of this spiritual message involving the river of the water of life and the tree of life.

Water in the life of plants

The bodies of plants are composed primarily of water.  In most non-woody plants, water is 85-95% of the plant’s weight.  In woody plants, the water content of wood accounts for up to 75% of the weight of a living tree.  Plants, when dried, weigh only a fraction of what they are alive.  Anyone who has dealt with a freshly fallen tree knows how heavy fresh cut logs can be.  Wait a year, until the water has evaporated, and they are much easier to handle.  The reason plants wilt is that much of their structural support involves water, or more specifically the pressure produced by water.  Plant cell structure is maintained by turgor pressure inside of the cells; the force of water inside of the cells pushing outward against the cell wall (a useful analogy is the pressure inside an inflated balloon giving the balloon it’s shape, or the air pressure inside of a tire).  

Most plants are composed of roots, stems, and leaves.  Plants obtain water from the soil through the roots.  Water travels up a plant through the roots, stem, branches, and leaves.  This is accomplished via a tissue type (vascular tissue) composed of hollowed out connected columnar cells (xylem) which form a sort of plumbing pipe system throughout the plant.  Water doesn’t enter through the above ground portions of the plant – the plant’s surface is covered with a waxy layer (cuticle) to protect the surfaces from the environment and help retain water in the plant.

The stem supports the above ground parts of the plant and serves as a conduit for the transport of water from the roots to the leaves.  The leaves are involved in two critical functions, providing the plant with energy in the form of sugars through the process of photosynthesis, and providing a means for water to be drawn up the plant against the force of gravity utilizing a process called transpiration, the loss of water vapor from the surfaces of the leaves through tiny pores called stomata.  It is necessary to lose water in order to draw more water into the plant from the soil.  This has to do with two general concepts in chemistry:  diffusion of a substance (a substance naturally moves from areas of higher concentration to areas of lower concentration), and the stickiness of water (water molecules are polar, meaning they behave as if they have a weak magnetic attraction to one another).  This stickiness is called cohesion.

Source: https://studyrocket.co.uk/revision/gcse-biology-triple-aqa/triple-organisation/transpiration 

The process of water moving up through a plant (against the force of gravity) is similar to what happens when a beverage is drunk through a straw.  Sucking on the straw creates tension on the beverage (tension is also called negative pressure).  The molecules of the beverage are chemically bound to one another due to their polarity (cohesion).  The combination of the tension produced by sucking on the straw and the cohesion of the beverage molecules creates a moving column of beverage up the straw.  This is basically what happens in the plant.  The atmosphere around a plant usually contains a lower concentration of water molecules, than what is inside the plant.  By diffusion, water moves from the plant into the atmosphere through the stomata (the process of transpiration).  As transpiration from leaf surfaces occurs, tension (negative pressure) is created in cells of the vascular tissue, while the cohesion of water molecules in the vascular cells causes it to move upwards towards the source of the tension (the evaporation of water from the leaf surface).  Basically, water is pulled up the plant; water molecules being “chain-linked” together due to their polarity (stickiness).

Source:  http://www.ontrack-media.net/gateway/biology/g_bm4l4as2.html

During times of normal function, plants transpire a tremendous amount of water.  The stomata (pores) through which water exits a plant, cover the leaf surfaces in great abundance.  Plant leaves contain between 1,000 to 100,000 stomata per square centimeter.  A single cabbage leaf, for example, contains over 11 million stomata!  The inset of this image shows a microscopic view of several stomata.

Source and license information:  https://asknature.org/strategy/guard-cells-regulate-gas-and-moisture-exchange/

More than 95% of water absorbed by a plant is returned to the atmosphere through transpiration within a few hours.  On an average summer day, a full sized maple tree can transpire over 50 gallons (200 liters) of water an hour. In a single week, a one acre lawn can transpire over 26,000 gallons (100,000 liters) of water.  In the Amazon, half of the rainfall is moisture derived from transpiration. One of the problems of large-scale deforestation is the change in precipitation patterns that it can cause.

Light in the life of plants

Stomata serve two essential functions for plants.  They are essential to a plant’s ability to absorb water, and move it throughout its body.  Additionally, stomata are essential for a process called gas exchange, essential to photosynthesis.  The process of photosynthesis involves the production of sugars from two simple raw materials, water and carbon dioxide.  Plants use sugars, just like we do – as a source of energy to maintain life, and what isn’t used immediately is stored in thickened root structures (like potato tubers or enlarged carrot taproots), or in fruit (many fruits taste sweet due to the stored sugars they contain).  Leaves acquire the carbon dioxide they need for photosynthesis from the atmosphere, through their stomatal pores.  As photosynthesis takes place, oxygen gas is produced, and diffuses out of the plant through the stomata.

Stomata can be open, allowing for water to exit, and for carbon dioxide and oxygen to move in and out of the plant, or they can be closed.  Each stomatal pore is surrounded by two cells called guard cells, which function to control the opening and closing of the pore, in response to a plant’s water and carbon dioxide needs.  Here is a one minute video of an actual stomata closing.

Exposure to sunlight triggers stomata to open.  As a plant’s leaves absorb light energy, which initiates the process of photosynthesis, there is a need for both carbon dioxide and water (both utilized as ingredients in the photosynthetic production of sugar).  Open stomata are needed to allow water to be drawn up the plant body from soil, through the roots, stem, and branches, into the leaves. The open stomata also allows carbon dioxide to diffuse into the leaves from the surrounding atmosphere.  During periods of darkness, stomata close, as there is no photosynthesis, and therefore no need for carbon dioxide.  During times of water stress (low soil moisture, very hot and sunny days, drought), plants will close their stomata to minimize water loss.  If a plant cannot absorb a sufficient amount of water, it will wilt as the cells in the plant lose turgor pressure.  A wilted plant is unable to perform its normal functions – the process of photosynthesis is impaired, as it requires water to proceed.  If deprived of water long enough, the plant will die.

The importance of water to a plant cannot be overstated.  Water is the primary factor that limits plant growth in most areas.  Water carries the mineral nutrients required for making all sorts of molecules used as basic building blocks in the cells, and molecules used to run the basic processes of the cells.  Water is needed for the process of photosynthesis to occur.  Plants are dependent on photosynthesis for their energy.  Water is required to maintain turgor in all of plant’s cells (it keeps the cells inflated), which is necessary for the plant to function normally.  Water is the most abundant molecule found in plants.  While, water accounts for 85-95% of the weight of most plants, 95% of the water absorbed by a plant is transpired back into the atmosphere.

The movement of water up through a plant, initially from the soil, into the root, through the stem, branches and leaves, and then either used in photosynthesis to make sugar, or exit the plant through the stomata occurs automatically (by default), requiring no effort, or action, so long as the stomata on its leaves are open.  When are the stomata open?  In the presence of sunlight.  When there is light, there is automatic movement of water through the plant.

Spiritual water and light

Let’s go back to John, 7:37-39

On the last and greatest day of the festival, Jesus stood and said in a loud voice, “Let anyone who is thirsty come to me and drink.  Whoever believes in me, as Scripture has said, rivers of living water will flow from within them.” By this he meant the Spirit, whom those who believed in him were later to receive. Up to that time the Spirit had not been given, since Jesus had not yet been glorified.

Isn’t it interesting, that Jesus refers to water flowing out of people who come to him, which is actually what happens in plants?  And shortly afterwards, Jesus is speaking to a crowd.  John 8:12 says

When Jesus spoke again to the people, he said, “I am the light of the world. Whoever follows me will never walk in darkness, but will have the light of life.”

It’s light which triggers a plant to open its stomata, so that water can move through the plant.  It’s light which initiates the process of photosynthesis which provides the plant its sole source of food.  Here in John, we have Jesus speaking of spiritual water and spiritual light.  And in the Book of Revelation we have a tree positioned next to the river of the water of life whose leaves are for the healing of the nations.  Think about that for a moment.

The next post will cover other Bible passages making use of plant analogies to convey spiritual truths about how God designed us to function as spiritual creations.